Once you have figured out the difference between Great Britain and the United Kingdom, you can move on to learning how the kingdom became united. Three “Acts of Union” are the key. The U.K. flag, the Union Jack, is a great visual aid for keeping the story straight, but the story started a long time before the flag came into existence at the beginning of the 17th century.
In 1284 the crown of England annexed Wales under the Statute of Wales. But annexation and incorporation are two different matters, and the Act of Union of 1536 declared English King Henry VIII’s wish to incorporate Wales within his realm. The Welsh were to be accorded the same political status as the English and to send representatives to Parliament. In with English common law, out with Welsh law. None of this came into effect until 1543, however, when all the details were laid out in a second act. Still, Wales and England had been unified.
Sixty years later, England and Scotland were still entirely independent kingdoms when Queen Elizabeth I of England died unmarried and childless in 1603. Her cousin James VI, who happened to be the king of Scotland, also became the king of England as James I under what became known as the union of the crowns. He was determined to bring the two kingdoms together into a single British state. Failing to achieve that goal, he contented himself with their symbolic unification in the creation of a flag in 1606 that bore both the English cross of St. George and the Scottish cross of St. Andrew. That banner, the forerunner of the United Kingdom’s familiar flag, took its name, the Union Jack, from the shortened form of the name Jacobus, the Latin version of James.
For most of the 17th century, against the backdrop of the English Civil Wars, the Restoration, and the Glorious Revolution, England and Scotland remained under the rule of the same monarch, but repeated efforts to unite the two kingdoms were unsuccessful (save for Oliver Cromwell’s brief unification, maintained by an English army of occupation in Scotland during the Protectorate). Finally, at the beginning of the 18th century, Scotland needed economic help, and England needed a safeguard against the possibility of Scotland serving as a launching ground for French attacks. The English also feared a Jacobite attempt to restore the crown to Queen Anne’s exiled Roman Catholic half-brother, James Edward, the Old Pretender. Unification posed an answer for both kingdoms’ problems. Free and equal trade throughout the new unified kingdom would be Scotland’s payoff. In return, England would get Scotland’s acquiescence in the Hanoverian succession, through which Protestant rule would be maintained by the accession to the throne of George I. Scotland had to relinquish its parliament under the agreement, but it kept Scottish law. Thus, the 1707 Act of Union, which went into effect on May 1, 1707, creating the Kingdom of Great Britain, was a winning deal on both sides of the border.
Not everyone in Scotland was happy with the “British” administration of their home (which contributed to the staging of the failed Jacobite rebellions of 1715 and 1745), but there was a clear difference between Scotland’s partnership with England and the restricted relationship Ireland had with Great Britain. The Irish Rebellion of 1798 and the fear that Ireland would be the launchpad for a French invasion led British Prime Minister William Pitt the Younger to believe that the best solution to the problem was another union, this time between Great Britain and Ireland. Pitt argued that the union would help develop Ireland economically. He also claimed (wrongly) that it would make it easier to grant concessions to the Roman Catholics (who would become a minority in the new United Kingdom). The British government overcame strong resistance to unification by nakedly buying enough votes to secure majorities in both the British and Irish houses for passage of yet another Act of Union on March 28, 1800. The Act of Union that created the United Kingdom of Great Britain and Ireland came into effect on January 1, 1801. This union remained in place 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 December 6, 1921, following the Irish War of Independence (Anglo-Irish War, 1919–21). The union officially ended on January 7, 1922, when the treaty was ratified by the Dáil.
Finally, on May 29, 1953, by proclamation, Elizabeth II became known as queen of the United Kingdom of Great Britain and Northern Ireland.