Of mixed English and American parentage, Churchill was born in Oxfordshire to a wealthy, aristocratic family. He joined the British Army in 1895, and saw action in British India, the Anglo–Sudan War, and the Second Boer War, gaining fame as a war correspondent and writing books about his campaigns. Elected an MP in 1900, initially as a Conservative, he defected to the Liberals in 1904. In H. H. Asquith's Liberal government, Churchill served as President of the Board of Trade, Home Secretary, and First Lord of the Admiralty, championing prison reform and workers' social security. During the First World War, he oversaw the Gallipoli Campaign; after it proved a disaster, he resigned from government and served in the Royal Scots Fusiliers on the Western Front. In 1917, he returned to government under David Lloyd George as Minister of Munitions, then as Secretary of State for War and Air, and finally for the Colonies, overseeing the Anglo-Irish Treaty and Britain's Middle East policy. After two years out of Parliament, he served as Chancellor of the Exchequer in Stanley Baldwin's Conservative government, returning the pound sterling in 1925 to the gold standard at its pre-war parity, a move widely seen as creating deflationary pressure and depressing the UK economy.
 
Out of office during the 1930s, Churchill took the lead in calling for British rearmament to counter the growing threat from Nazi Germany. At the outbreak of the Second World War he was re-appointed First Lord of the Admiralty. In 1940 he became prime minister, replacing Neville Chamberlain. Churchill oversaw British involvement in the Allied war effort against Germany and the Axis powers.