Premiership of Margaret Thatcher

Margaret Thatcher's tenure as Prime Minister of the United Kingdom began on 4 May 1979 when she accepted an invitation from Queen Elizabeth II to form a government, succeeding James Callaghan of the Labour Party, and ended on 28 November 1990 upon her resignation. Thatcher, who had been Leader of the Conservative Party since her election in 1975, had led the Conservative Party to victory at the 1979 general election, and won landslide re-elections for the party in 1983 and in 1987. She was the longest-serving British prime minister of the 20th century and the first woman to hold the office. As prime minister Thatcher also served simultaneously as First Lord of the Treasury and Minister for the Civil Service.

In domestic policy Thatcher implemented sweeping reforms concerning the affairs of the economy, eventually including the privatisation of most nationalised industries, and the weakening of trade unions. She emphasised reducing the government's role and letting the marketplace decide in terms of the neoliberal ideas pioneered by the economists Milton Friedman and Friedrich Hayek, promoted by her mentor Keith Joseph, and promulgated by the media as Thatcherism. In foreign policy Thatcher decisively defeated Argentina in the Falklands War in 1982, and worked with the United States president Ronald Reagan to actively oppose Soviet communism during the Cold War, but also promoted collaboration with the Soviet leader Mikhail Gorbachev in ending the Cold War.

In the first years of her premiership, she had a deeply divided cabinet. As the leader of the "dry" faction in the party, she purged most of the one-nation "wet" Conservatives and took full control. However, by the late 1980s she had alienated several senior members of her Cabinet with her opposition to greater economic integration into the European Economic Community, which she argued would lead to a federalist Europe and surrender Britain's ability to self-govern. She also alienated many Conservative voters and parliamentarians with the imposition of a local poll tax. As her support ebbed away, she was challenged for her leadership in 1990 and persuaded by her Cabinet to withdraw from the second round of voting, ending her eleven-year premiership. She was succeeded by John Major, her Chancellor of the Exchequer.