(May 1, 1707), treaty that effected the union of England and Scotland under the name of Great Britain.

Since 1603 England and Scotland had been under the same monarchs. After revolutions in 1688–89 (see Glorious Revolution) and 1702–03, projects for a closer union miscarried, and in 1703–04 international tension provoked a dangerous legislative warfare between the separate parliaments of England and Scotland. On both sides of the border, however, statesmen were beginning to realize that an incorporating union offered the only mutually acceptable solution to a problem that had suddenly become urgent: Scotland's need for economic security and material assistance and England's need for political safeguards against French attacks and a possible Jacobite restoration, for which Scotland might serve as a conveniently open back door. England's bargaining card was freedom of trade; Scotland's was acquiescence in the Hanoverian succession. Both points were quickly accepted by the commissioners appointed by Queen Anne to discuss union, and within three months they had agreed on a detailed treaty (April–July 1706).

The two kingdoms were to be united, the Protestant succession was adopted, and trade was to be free and equal throughout Great Britain and its dominions. Subject to certain temporary concessions, taxation, direct and indirect, would also be uniform; and England compensated Scotland for undertaking to share responsibility for England's national debt by payment of an equivalent of £398,085 10 shillings. Scots law and the law courts were to be preserved. In the united Parliament, Scotland, because of its relative poverty, was given the inadequate representation of 45 commoners and 16 lords. By separate statutes annexed to the treaty, the Presbyterian Church of Scotland and the Episcopal Church of England were secured against change.

With only minor amendments the Scottish Parliament passed the treaty in January 1707, and the English passed it soon after. The royal assent was given on March 6, and the union went into effect on May 1, 1707.

(Jan. 1, 1801), legislative agreement uniting Great Britain (England and Scotland) and Ireland under the name of the United Kingdom of Great Britain and Ireland.

The Irish Rebellion of 1798 brought the Irish question forcibly to the attention of the British Cabinet; and William Pitt (Pitt, William, The Younger) the Younger, the British prime minister, decided that the best solution was a union. By legislative enactments in both the Irish and the British parliaments, the Irish Parliament was to be abolished, and Ireland thenceforth was to be represented at the Parliament in Westminster, London, by 4 spiritual peers, 28 temporal peers, and 100 members of the House of Commons. A union, Pitt argued, would both strengthen the connection between the two countries and provide Ireland with opportunities for economic development. It would also, he thought (mistakenly), make it easier to grant concessions to the Roman Catholics, since they would be a minority in a United Kingdom. Naturally the union met with strong resistance in the Irish Parliament, but the British government, by the undisguised purchase of votes, either by cash or by bestowal of honours, secured a majority in both the British and Irish Houses that carried the union on March 28, 1800. The Act of Union received the royal assent on Aug. 1, 1800, and it came into effect on Jan. 1, 1801. Henceforth, the monarch was called the king (or queen) of the United Kingdom of Great Britain and Ireland.

The union remained until the recognition of the Irish Free State (excluding six of the counties of the northern province of Ulster) by the Anglo-Irish treaty concluded on Dec. 6, 1921. The union officially ended on Jan. 15, 1922, when it was ratified by the Provisional Government led by Michael Collins in Ireland. (On May 29, 1953, by proclamation, Elizabeth II became known as queen of the United Kingdom of Great Britain and Northern Ireland.)