originally, in U.S. history, the attempt to take over countries at peace with the United States via privately financed military expeditions, a practice that reached its peak during the 1850s. In U.S. legislative usage, the term refers to obstructive delaying tactics (see filibuster).

Spurred by land hunger and by the desire of proslavery Southerners to add future slave states to the Union, filibusterers were active during the decade prior to the American Civil War. Starting in 1849, Narcisco López led three unsuccessful expeditions against Cuba. He convinced many prominent Southerners that the island was ripe for revolt against Spain. In his last attempt (1851), López landed in Havana with a contingent of Southern volunteers. The expected popular uprising against Spain failed to materialize, and López, along with about 50 Southerners, was executed by Spanish military authorities.

The high point of American filibustering was reached under William Walker (Walker, William), a Californian who first tried to take Mexican Baja (Lower) California and then turned his attention to Nicaragua. In 1855 Walker took advantage of a civil war in Nicaragua to take control of the country and set himself up as dictator. In May 1856 President Franklin Pierce recognized the Walker regime.

Walker was undone, however, when he tried to seize control of the Accessory Transit Company (an American transport company in Nicaragua) from Cornelius Vanderbilt (Vanderbilt, Cornelius). Vanderbilt formed a coalition of Central American states against Walker, and the dictator of Nicaragua was forced to surrender (May 1, 1857). Walker tried twice more to take Nicaragua. On his last attempt in 1860 he was captured on the coast of Honduras and put before a British firing squad.

Filibustering came to an end with the start of the American Civil War. Land hunger was never quite so strong again as the United States turned from an agrarian to an industrial nation. With the abolition of slavery, Southern support for such conquests disappeared.