lion people engaged across much of its empire and several regions of Europe, and increasingly took a major role on the Western front. The nation suffered some two and a half million casualties and finished the war with a huge national debt. After the war the United Kingdom received the League of Nations mandate over former German and Ottoman colonies, and the British Empire had expanded to its greatest extent, covering a fifth of the world's land surface and a quarter of its population. The rise of Irish Nationalism and disputes within Ireland over the terms of Irish Home Rule led eventually to the partition of the island in 1921, and the Irish Free State became independent with Dominion status in 1922, while Northern Ireland remained part of the United Kingdom. The Great Depression (1929–32) occurred when the UK had not recovered from the effects of the war, and led to hardship as well as political and social unrest.
The United Kingdom was one of the Allies of World War II and an original signatory to the Declaration of the United Nations. Following the defeat of its European allies in the first year of the war, the United Kingdom continued the fight against Germany, notably in the Battle of Britain and the Battle of the Atlantic. After the victory, the UK was one of the Big Three powers that met to plan the postwar world. The war left the country financially damaged. Marshall Aid and loans from both the United States and Canada helped the UK on the road to recovery.
The Labour government in the immediate post-war years initiated a radical programme of changes, with a significant impact on British society in the following decades. Domestically, major industries and public utilities were nationalised, a Welfare State was established, and a comprehensive publicly funded healthcare system, the National Health Service, was created. In response to the rise of local nationalism, the Labour government's own ideological sympathies and Britain's now