in warfare, the science or art of employing all the military, economic, political, and other resources of a country to achieve the objects of war.

The term strategy derives from the Greek strategos, an elected general in ancient Athens. The strategoi were mainly military leaders with combined political and military authority, which is the essence of strategy. Because strategy is about the relationship between means and ends, the term has applications well beyond war: it has been used with reference to business, the theory of games, and political campaigning, among other activities. It remains rooted, however, in war, and it is in the field of armed conflict that strategy assumes its most complex forms.

Such, at least, has been primarily the view articulated by the greatest of all Western military theoreticians, the Prussian general Carl von Clausewitz (Clausewitz, Carl von). In his classic strategic treatise, On War (1832), Clausewitz emphasizes the uncertainty under which all generals and statesmen labour (known as the “fog of war”) and the tendency for any plan, no matter how simple, to go awry (known as “friction”). Periodically, to be sure, there have been geniuses who could steer a war from beginning to end, but in most cases wars have been shaped by committees. And, as Clausewitz says in an introductory note to On War, “When it is not a question of acting oneself but of persuading others in discussion, the need is for clear ideas and the ability to show their connection with each other”—hence the discipline of strategic thought.

Ancient Greece is a story of distinctive states and eminent leaders, such as Alexander the Great, whose triumphs against the Persian empire in the 4th century BC illustrate the success of strategies of overthrow against centralized states unable to recuperate from a severe setback. The rise of ancient Rome, on the other hand, is far more a story of institutions. From the Greek historian Polybius in the 2nd century BC to the Florentine political philosopher Niccolò Machiavelli (Machiavelli, Niccolò) in the 15th–16th century, the story of Roman strategy seems one of a collective approach to war rather than a reflection of the choices of a single statesman. Rome's great strength, the ancient historians argue (and modern historians seem to agree), stemmed from political institutions that turned internal divisions into an engine of external expansion, that allowed for popular participation and executive decision, and that concentrated strategic decision making in a powerful Senate composed of the leading men of Rome. To its unique political constitution was added the Roman legion, a form of military organization far more flexible and disciplined than anything the world had yet seen—a fabulous tool for conquest and, in its attention to detail, from the initial selection of soldiers to their construction of camps to their rotation on the battle line, a model imitated in succeeding centuries.

Rome's conquest of the Mediterranean world illustrates the idea of a tacit or embedded strategy. Rome's ruthlessness in dividing its enemies, in creating patron-client relationships that would guarantee its intervention in more civil wars, its cleverness in siding with rebels or dissidents in foreign states, and its relentlessness in pursuing to annihilation its most serious enemies showed remarkable continuity throughout the republic.

The Second Punic War (Punic War, Second) (218–201 BC) illustrates these propositions well. There were only two leading figures of note in Rome throughout the war: Quintus Fabius Maximus Verrucosus (Cunctator) (Fabius Maximus Verrucosus, Quintus), who delayed and bought time while Rome recovered from its initial disastrous defeats, and Scipio Africanus the Elder, who delivered the final blow of the Second Punic War to Carthage at the Battle of Zama (Zama, Battle of) (202 BC). It does not appear that either was the equal of Hannibal, the brilliant Carthaginian general who administered defeat after defeat to superior Roman armies on their home turf. More important than personalities, however, was Rome's unflinching determination to pursue its enemies, quite literally to the death. Hannibal was cornered in the Bithynian (Bithynia) village of Libyssa and committed suicide, following a demand from Rome that he be turned over by Antiochus III of Syria, whom he had aided in rebellion against Rome following the defeat of Carthage. And Carthage itself—long the target of the grim senator Marcus Porcius Cato (Cato, Marcus Porcius)'s insistence that it be destroyed (he famously took to ending every oration with the words “Ceterum censeo delendam esse Carthaginem,” which translate as “Besides which, my opinion is that Carthage must be destroyed”)—was wiped out of existence in the Third Punic War (Punic War, Third) (149–146 BC), which was provoked by Rome for the purpose of finishing off its most dangerous potential opponent.

Most military histories skim over the Middle Ages, incorrectly believing it to be a period in which strategy was displaced by a combination of banditry and religious fanaticism. Certainly, the sources for medieval strategic thought lack the literary appeal of the classic histories of ancient Greece and Rome. Nevertheless, Europe's medieval period may be of especial relevance to the 21st century. In the Middle Ages there existed a wide variety of entities—from empires to embryonic states to independent cities to monastic orders and more—that brought different forms of military power to bear in pursuit of various aims. Unlike the power structures in the 18th and 19th centuries, military organizations, equipment, and techniques varied widely in the medieval period: the pikemen (pike) of Swiss villages were quite different from the mounted chivalry of western Europe, who in turn had little in common with the light cavalry of the Arabian heartland. The strategic predicament of the Byzantine Empire—beset by enemies that ranged from the highly civilized Persian and Arab empires to marauding barbarians—required, and elicited, a complex strategic response, including a notable example of dependence on high technology. Greek fire, a liquid incendiary agent, enabled the embattled Byzantine Empire to beat off attacking fleets and preserve its existence until the early 15th century.

The story was different in East and Central Asia, particularly in China, where the mobility and discipline of Mongol armies (to take only the most notable example) and the relatively open terrain allowed for the making and breaking not only of states but of societies by mobile cavalry armies bent on conquest and pillage. Strategy emerged in the contest for domestic political leadership (as in Oda Nobunaga's unification of much of Japan during the 16th century) and in attempts either to limit the irruptions of warlike nomads into civilized and cultivated areas or to expand imperial power (as in the rise of China's Qing dynasty in the 17th century). However, after the closure of Japan to the world at the end of the 16th century and the weakening of the Qing dynasty in the 19th century, strategy became more a matter of policing and imperial preservation than of interstate struggle among comparable powers. It was in Europe that a competitive state system, fueled by religious and dynastic tensions and making use of developing civilian and military technologies, gave birth to strategy as it is known today.

The development of state structures, particularly in western Europe, during the 16th and 17th centuries gave birth to strategy in its modern form. “War makes the state, and the state makes war,” in the words of American historian Charles Tilly. The development of centralized bureaucracies and, in parallel, the taming of independent aristocratic classes yielded ever more powerful armies and navies. As the system of statecraft gradually became secularized—witness the careful policy pursued by France under the great cardinal Armand-Jean du Plessis, duc de Richelieu (Richelieu, Armand-Jean du Plessis, cardinal et duc de), chief minister to King Louis XIII from 1624 to 1642, who was willing to persecute Protestants at home while supporting Protestant powers abroad—so too did strategy become more subtle. The rapine and massacre of the Thirty Years' War (1618–48) yielded to wars waged for raison d'état, to aggrandize the interests of the ruler and through him the state. In this as in many other ways, the early modern period witnessed a return to Classical roots. Even as drill masters studied ancient Roman textbooks to recover the discipline that made the legions (legion) formidable instruments of policy, so too did strategists return to a Classical world in which the logic of foreign policy shaped the conduct of war.

Strategy began to seem more like technique than art, science rather than craft. Practitioners, such as the 17th-century French engineer Sébastien Le Prestre de Vauban (Vauban, Sébastien Le Prestre de) and the 18th-century French general and military historian Henri, baron de Jomini (Jomini, Henri, baron de), began to make of war an affair of rules, principles, and even laws. Not surprisingly, these developments coincided with the emergence of military schools and an increasingly scientific and reforming bent—artillerists studied trigonometry, and officers studied military engineering. Military literature flourished: Essai général de tactique (1772), by Jacques Antoine Hippolyte, comte de Guibert, was but one of a number of thoughtful texts that systematized military thought, although Guibert (unusual for writers of his time) had inklings of larger changes in war lying ahead. War had become a profession, to be mastered by dint of application and intellectual, as well as physical, labour.

The author who understood this best was the Prussian (Prussia) Carl von Clausewitz (Clausewitz, Carl von), whose military experience spanned the years from 1793 to 1815, a period in which Europe was convulsed by a series of wars centring on France. The Prussian general's masterpiece On War (1832) appeared shortly after his death. It described an approach to strategy that would, with modifications, last at least through the middle of the 20th century.

The wars of the mid-19th century, in particular the wars of German unification (Germany) (Prussia's wars with Denmark, Austria, and France in 1864, 1866, and 1870–71, respectively) and the American Civil War (1861–65), marked a peak of Clausewitzian strategy. German (Germany) Chancellor Otto von Bismarck (Bismarck, Otto von) and U.S. Pres. Abraham Lincoln (Lincoln, Abraham) successfully waged war for great stakes. Exemplary Clausewitzian leaders, they used the new instruments of the time—the mass army, now sustained year-round by early industrial economies that could ship vast quantities of matériel to distant fronts—to achieve their purposes.

Compounding these challenges was the advent of technology as an important and distinct element in war. The 18th century had experienced great stability in the tools of war, on both land and sea. The musket of the early 18th century did not differ materially from the firearm carried into battle by one of the duke of Wellington (Wellington, Arthur Wellesley, 1st duke of, marquess of Douro, marquess of Wellington, earl of Wellington, Viscount Wellington of Talavera and of Wellington, Baron Douro or Wellesley)'s British soldiers 100 years later; similarly, British Adm. Horatio Nelson (Nelson, Horatio Nelson, Viscount)'s flagship HMS Victory at the Battle of Trafalgar (Trafalgar, Battle of) (1805) had decades of service behind it before that great contest. But by the mid-19th century this had changed. On land the advent of the rifle—modified and improved by the development of breech loading, metal cartridges, and later smokeless gunpowder—was accompanied as well by advances in artillery and even early types of machine guns (machine gun). At sea changes were even more dramatic: steam replaced sail, and iron and steel replaced wood and canvas. Obsolescence now occurred within years, not decades, and technological experts assumed new prominence.

It was during World War I that technological (military technology) forces yielded a crisis in the conduct of strategy and strategic thought. Mass mobilization and technologies that had outpaced the abilities of organizations to absorb them culminated in slaughter and deadlock on European battlefields. How was it possible to make war still serve political ends? For the most part, the contestants fell back on a grim contest of endurance, hoping that attrition—a modern term for slaughter—would simply cause the opponents' collapse and a victory by diktat. Only the British attempted large-scale maneuvers: by launching campaigns in several peripheral theatres, including the Middle East, Greece, and most notably Turkey. These all failed, although the last—a naval attack and then two amphibious assaults on the Gallipoli Peninsula (see Dardanelles Campaign)—had moments of promise. These reflected, at any rate, a strategic concept other than attrition: the elimination of the opposing coalition's weakest member. In the end, though, the war hinged on the main contest on the Western Front. It was there, in the fall of 1918, that the struggle was decided by the collapse of German forces after two brilliant but costly German offensives in the spring and summer of that year, followed by a remorseless set of Allied counterattacks.

The brute strategy of attrition did not mean a disregard of the advantages offered by technology. The combatants turned to every device of modern science—from radio to poison gas, machine gun to torpedo, the internal combustion engine to aviation—to improve their abilities to make war. Peace arose, nonetheless, as a result of exhaustion and collapse, not an adroit matching of means to ends. Technology tantalized soldiers with the possibility of a decisive advantage that never materialized, while the passions of fully mobilized populations precluded compromise agreements that might have rescued the bleeding countries of Europe from their suffering.

Still, the keynote of the period leading up to World War II was the quest for a technological remedy to the problem of deadlock. Armoured (armoured vehicle) warfare had its proponents, as did aerial bombardment. Tanks (tank) and airplanes had made a tentative debut during World War I, and, had the war lasted a little longer, they certainly would have demonstrated abilities well beyond those that were shown during the war. The advocates of armoured warfare resided for the most part in Britain, which pioneered the creation of experimental armoured forces in the early 1920s. J.F.C. Fuller (Fuller, J F C) in particular, a brilliant but irascible major general and the architect of what would have been the British Army's war plan in 1919, made a powerful case that tanks, supported by other arms, would be able to achieve breakthroughs and rapid advances unheard of throughout most of the Great War. His voice was echoed in other countries. One such prophet was a French colonel who had spent most of the war in a German prisoner-of-war camp. Charles de Gaulle (Gaulle, Charles de)'s plea for a mechanized French army (The Army of the Future; 1934) fell on deaf ears not so much because the French army opposed tanks (it did not) but rather because he called for a small, professional, mechanized army capable of offensive action. France's military and political leaders, accustomed to an army that had a long and deeply ingrained conscript tradition, and preferring a strategic posture of defense against invasion, was uninterested.

air warfare was a different matter. Aircraft had proven invaluable during World War I for a variety of missions—reconnaissance, artillery spotting, strafing, bombing, and even transport. All major powers rushed to acquire a variety of combat aircraft and to experiment with new types. At sea the question was one of developing the right techniques and procedures as well as technology for operating aircraft carriers (aircraft carrier). On land the issue became one of the role of aerial bombardment.

The new weapons and operational doctrines—that is, the combination of organization and techniques embodied in the armoured division on land or the carrier task force at sea—were tested in World War II. This conflict represented the culmination of trends in strategic thought and behaviour manifest since the early 19th century. The mobilization of populations had become not merely total but scientific: governments managed to squeeze the last ounce of effectiveness out of men and women of all ages, who endured rationing, extended workweeks, and protracted military service to an extent unimaginable even 30 years before. Those governments that were most efficient at doing so—the U.S., the British, and to some extent the Soviet (Union of Soviet Socialist Republics)—defeated those that were less relentlessly rational. It was, ironically perhaps, the United States and Britain that adopted large-scale mobilization of women in war production and auxiliary military service, while Germany and Japan flinched at such an upheaval in social roles. In some cases, older attitudes to war, most notably a Japanese warrior ethic that paid little heed to mundane matters such as logistics or field medicine, proved dysfunctional. German and Japanese strategy often emanated from wild ideological beliefs, leading to debacles when sheer will proved unequal to carefully amassed and directed resources on the other side. As a result, strategy as a rational mode of thought seemed to triumph.

The new tools of warfare worked well, though not quite as expected. Attacks on cities and economic targets proved brutally effective, but only over time. The contest between offense and defense continued, and military leaders discovered that air forces had to win a battle against opposing airmen before they could deliver crushing force against an opponent's civilian population. On land, new formations built around the tank increased the speed of warfare and delivered some extraordinary outcomes—most notably, the overthrow of France in 1940 in a campaign that was decided in less than two weeks of hard fighting and completed in less than two months.

The development of machine-centred warfare had restored mobility to the battlefield; science and the arts of administration had allowed those techniques to be fully applied; and modern politics meant that the goals of war had become not the seizure of isolated provinces for barter but nothing less than the survival of states and even peoples. Every auxiliary science and discipline, from weather forecasting to electronics, from abstruse forms of mathematics to modern advertising, was mobilized to its fullest. At the pinnacle, the governments that won the war did so with large, highly skilled organizations that brought together soldiers and civilians and that concluded many of the war's largest decisions in international conferences supported by hundreds, indeed thousands, of support personnel. Strategic decisions—the launching of the Anglo-American invasion of Normandy (Normandy Invasion) on June 6, 1944, for example—emerged through carefully weighed calculations of many kinds, from soil engineering to the intricacies of coalition politics.

The period from 1939 to 1945 represented the acme of the old style of war, and with it strategy as the purposeful practice of matching military might with political objectives. In its aftermath a number of challenges to this classical paradigm of war emerged, the first in the closing days of World War II. The dropping of atomic bombs (atomic bomb) on Hiroshima and Nagasaki, Japan, inaugurated a new era of war, many observers felt. Bernard Brodie, an American military historian and pioneering thinker about nuclear weapons, declared in 1946:Thus far the chief purpose of our military establishment has been to win wars. From now on its chief purpose must be to avert them. It can have almost no other useful purpose.

In all cases, the centre of gravity lay with the problem of deterrence, the prevention of adverse enemy behaviours rather than concrete measures to block, reverse, or punish them. Strategic thought now entered a wilderness of mirrors: What behaviour could be deterred, and what could not? How did one know when deterrence had worked? Was it bad to defend one's population in any way—with civil defense or active defenses such as antiballistic missiles—because that might weaken mutual deterrence? The problem became more grave as additional countries acquired nuclear weapons: Were Chinese leaders deterred by the same implicit threats that worked on U.S. and Soviet leaders? For that matter, did Indians and Pakistanis view each other in the same way that Americans and Soviets viewed each other?

It is likely (although in the nature of things, unprovable) that the looming presence of nuclear weapons prevented a U.S.-Soviet conflict during the Cold War. On the other hand, the highly probable possession of nuclear weapons by Israel in 1973 did not deter an Egyptian-Syrian conventional assault on that country, nor did Britain's nuclear arsenal prevent Argentina from invading the Falkland Islands in 1982 (see Falkland Islands War). For that matter, North Vietnam seems to have disregarded American nuclear weapons during the Vietnam War (1954–75).

Initially, nuclear strategy concerned only a handful of states: the United States, the Soviet Union, China, the United Kingdom, and France. These were countries embedded, initially at least, in Cold War alliances. In 1974 India tested a nuclear device; this was followed by competitive testing of weapons with Pakistan in 1998. Israel was understood to have acquired nuclear weapons during the 1970s if not earlier, and North Korea avowed its acquisition of at least one or two weapons in 2002. In 1991 it became apparent that Iraq had a vigorous and potentially successful nuclear program, and a similar Iranian program had been under way. The spread of nuclear weapons amounted effectively to a second nuclear revolution, which may have operated by a different logic than the first. The stylized (though nonetheless frightening) standoff of the Cold War was replaced by a world in which many of the same elaborate safeguards might no longer exist, by nuclear possession on the part of countries that routinely fought one another (particularly in the Asian subcontinent), and by the development of weapons small enough to be smuggled into a country in a variety of ways. By the beginning of the 21st century then, nuclear issues had revived as a subject of strategic concern, if not serious strategic thought. The proliferation of nuclear technology by a Pakistani scientist, Abdul Qadeer Khan, and the development of nuclear weapons by Kim Jong Il's North Korea shook optimistic assumptions about the ability of the interstate system to stop marginal actors from acquiring and spreading the wherewithal to make nuclear weapons—including the possibility of terrorist groups acquiring such weapons. The overt entry of India and Pakistan into the nuclear club, the generally acknowledged Israeli nuclear arsenal, and the looming Iranian nuclear threat were no less unsettling.

To be sure, the European powers had faced able opponents in the past, from the indigenous Native Americans (Native American) to the Marathas (see Maratha Wars (Marāṭhā Wars)) in India during the late 18th and early 19th centuries and Abdelkader in Algeria in the 1830s and to the Boer farmers (see South African War) at the turn of the 20th century. And in many ways the pattern for a successful anti-imperial force appeared shortly after the end of World War I in the form of the Irish Republican Army, which had an important role in convincing the British to end its rule in most of that island. By and large, though, the story of imperial warfare in the period before World War II was of protracted struggle leading to pacification and quiescence. Emilio Aguinaldo (Aguinaldo, Emilio) succumbed to the American forces in the Philippines in 1901 following a two-year rebellion; the caliph ʿAbd Allāh (successor to al-Mahdī (Mahdī, al-)) was swept away by British rifles and machine guns in the Sudan in 1898.

Revolutionary war started as a rural phenomenon, although, as in Algiers in 1957, it sometimes included particularly vicious bouts of armed struggle in cities. At the end of the 20th century it became more of an urban phenomenon. In countries as different as Uruguay, Algeria, Peru, and Israel, guerrilla war shifted (in many cases, it had not far to go) into pure terror directed against civilian populations. Yet here too the results often disappointed those hoping to overthrow a government or displace a population. Hiding in an apartment block differs greatly from hiding in a jungle or a wooded mountain: nature's creatures do not spy for, collaborate with, or confess to the forces of order, but human beings do.

Revolutionary warfare often uses terror for its purposes, but terrorism has its own logic, often quite different from that of national or political groups seeking to control a state. Politically motivated terrorism, defined as the use of violence against noncombatants for the purpose of demoralization and intimidation, is an extremely old phenomenon. However, the September 11 attacks on the United States in 2001 took terrorism to a new level and opened up the possibility of a different form of warfare than any known thus far. The al-Qaeda (Qaeda, al-) organization that launched the simultaneous attacks on New York City and Washington, D.C., which cost some 3,000 lives and inflicted tens of billions of dollars of damage to buildings and a larger economy (particular aviation), was no traditional terrorist organization. It had its home in many countries, particularly Taliban-run Afghanistan, but it was a nonstate organization. It had its senior echelon of leaders, but these could be replaced, and it operated chiefly through terror cells proliferated around the world that could reconstitute and reshape themselves. Its aspirations, as portrayed in Osama bin Laden (bin Laden, Osama)'s declaration in February 1998 of “jihad against Jews and Crusaders,” were vast and religiopolitical in nature. Al-Qaeda was, moreover, a truly global organization whose members traveled easily in a cosmopolitan world in which no place on the planet was much more than 36 or 48 hours traveling time from any other. They communicated with one another using the Internet and cellular telephones, and they reacted to international developments as portrayed on the mushrooming 24-hour-a-day, seven-day-a-week television and other news media of the new century.

Edward Mead Earle, Gordon A. Craig, and Felix Gilbert (eds.), Makers of Modern Strategy: Military Thought from Machiavelli to Hitler (1941, reissued 1971), remains a most competent anthology on the development of the military mind and art. Its worthy successor is Peter Paret, Gordon A. Craig, and Felix Gilbert (eds.), Makers of Modern Strategy: From Machiavelli to the Nuclear Age (1986), which repeats three of the essays and provides more than 20 new ones. To both should be added Williamson Murray, MacGregor Knox, and Alvin Bernstein (eds.), The Making of Strategy: Rulers, States, and War (1994), which looks at strategy as a collective rather than an individual function.Among the classic texts of strategic thought, the two most important are Carl von Clausewitz, On War, ed. and trans. by Michael Howard and Peter Paret (1976, reissued 1989); and Sunzi, Sun Tzu: The Art of War: The First English Translation Incorporating the Recently Discovered Yin-ch'üeh-shan Texts, trans. by Roger T. Ames (1993). Geoffrey Blainey, The Causes of War, 3rd ed. (1988), is the best short modern introduction to the origins of wars. To these one should add the masterly collection of essays by Michael Howard, The Causes of War (1984); and, for a study on the relationship between politicians and generals in modern war, Eliot A. Cohen, Supreme Command: Soldiers, Statesmen, and Leadership in Wartime (2002).Thucydides, The Landmark Thucydides: A Comprehensive Guide to the Peloponnesian War (1996), is an excellent starting point for exploring the history of military strategy. Hew Strachan, The First World War, vol. 1, To Arms (2001), begins the monumental three-volume history covering strategy in World War I. For works that explore the full complexity of high command at the top, the reader should turn to broad military histories, such as the extraordinary British official history of strategy during World War II, Grand Strategy, 6 vol. in 7 (1956–76), a Her Majesty's Stationery Office publication; or the more limited Maurice Matloff and Edwin M. Snell, Strategic Planning for Coalition Warfare, 2 vol. (1953–59, reprinted 1968; vol. 1 also reissued separately, 1999), covering the years 1941–44. There are good accounts of strategic decision making in more recent conflicts in Michael B. Oren, Six Days of War: June 1967 and the Making of the Modern Middle East (2002); and Michael R. Gordon and Bernard E. Trainor, The Generals' War: The Inside Story of the Conflict in the Gulf (1995).Finally, the reader should not disregard the works about and by the makers of strategy themselves. In particular, Winston S. Churchill, Marlborough: His Life and Times, 6 vol. (1933–38, reissued 2002), is a strategical treatise masquerading as biography. Alan Brooke, Viscount Alanbrooke, War Diaries 1939–1945, ed. by Alex Danchev and Daniel Todman (2001), the dyspeptic memoirs of the head of the British Army during World War II, gives a useful window into the stresses of war at the top and an unwitting revelation of the difficulty of judging aright in the midst of war. Geoffrey Parker, The Grand Strategy of Philip II (1998), demonstrates that biographies from the early modern period and even before also can be studied with profit.Eliot A. Cohen