The Conservative Party was founded in 1834 from the Tory Party—giving rise to the Conservatives' colloquial name of Tories—and was one of two dominant political parties in the nineteenth century, along with the Liberal Party. During the 1890s, it formed a coalition government with the Liberal Unionist Party, a break-away faction of the Liberal Party. In 1912, the two parties merged to form the current Conservative and Unionist Party. In the 1920s, the Liberal vote greatly diminished and the Labour Party became the Conservatives' main rivals. Conservative Prime Ministers led governments for 57 years of the twentieth century, including Winston Churchill (1940–45, 1951–55) and Margaret Thatcher (1979–90). Thatcher's tenure led to wide-ranging economic liberalisation. The Conservative Party's domination of British politics throughout the twentieth century has led to them being referred to as one of the most successful political parties in the Western world.
The Conservatives are the third largest British party in the European Parliament, with eighteen MEPs, and sit with the European Conservatives and Reformists (ECR) parliamentary group. The party is a member of the Alliance of Conservatives and Reformists in Europe (ACRE) Europarty and the International Democrat Union (IDU).
The party is the second-largest in the Scottish Parliament and the second-largest in the Welsh Assembly. The Conservatives were formerly allied to the Ulster Unionist Party (UUP) in Northern Ireland but there is now a separate Northern Ireland Conservative party similar to the Welsh and Scottish Conservative parties. The party is also organised in the British Overseas Territory of Gibraltar.
The Conservative Party was founded in the 1830s. However some writers trace its origins to King Charles I in the 1620s. Other writers point to a faction, rooted in the 18th century Whig Party, that coalesced around William Pitt the Younger in the 1780s. They were known as "Independent Whigs", "Friends of Mr Pitt", or "Pittites" and never used terms such as "Tory" or "Conservative". Pitt died in 1806. From about 1812 on the name "Tory" was commonly used for a new party that according to historian Robert Blake "are the ancestors of 'Conservatism.'" Blake adds that Pitt's successors after 1812 "Were not in any sense standard-bearer's of 'true Toryism.'"
The term "Conservative" was suggested as a title for the party by a magazine article by J. Wilson Croker in the Quarterly Review in 1830. The name immediately caught on and was officially adopted under the aegis of Sir Robert Peel around 1834. Peel is acknowledged as the founder of the Conservative Party, which he created with the announcement of the Tamworth Manifesto. The term "Conservative Party" rather than Tory was the dominant usage by 1845.