Editing British Empire (section)

=== First World War ===
{{Main|History of the United Kingdom during the First World War}}

Britain's fears of war with Germany were realised in 1914 with the outbreak of the First World War. Britain quickly invaded and occupied most of Germany's overseas colonies in Africa. In the Pacific, Australia and New Zealand occupied [[German New Guinea]] and [[German Samoa]] respectively. Plans for a post-war division of the Ottoman Empire, which had joined the war on Germany's side, were secretly drawn up by Britain and France under the 1916 [[Sykes–Picot Agreement]]. This agreement was not divulged to the [[Hussein bin Ali, Sharif of Mecca|Sharif of Mecca]], who the British had been encouraging to launch an Arab revolt against their Ottoman rulers, giving the impression that Britain was supporting the creation of an independent Arab state.{{Sfn|Brown|1998|pp=494–495}}

The British declaration of war on Germany and its allies committed the colonies and Dominions, which provided invaluable military, financial and material support. Over 2.5&nbsp;million men served in the armies of the [[Dominion]]s, as well as many thousands of volunteers from the Crown colonies.{{Sfn|Marshall|1996|pp=78–79}} The contributions of Australian and New Zealand troops during the 1915 [[Gallipoli Campaign]] against the Ottoman Empire had a great impact on the national consciousness at home and marked a watershed in the transition of Australia and New Zealand from colonies to nations in their own right. The countries continue to commemorate this occasion on [[Anzac Day]]. Canadians viewed the [[Battle of Vimy Ridge]] in a similar light.{{Sfn|Lloyd|1996|p=277}} The important contribution of the Dominions to the [[war effort]] was recognised in 1917 by British prime minister [[David Lloyd George]] when he invited each of the Dominion prime ministers to join an [[Imperial War Cabinet]] to co-ordinate imperial policy.{{Sfn|Lloyd|1996|p=278}}

Under the terms of the concluding [[Treaty of Versailles]] signed in 1919, the empire reached its greatest extent with the addition of {{convert|1.8|e6sqmi|e6km2|abbr=unit}} and 13&nbsp;million new subjects.{{Sfn|Ferguson|2002|p=315}} The colonies of Germany and the Ottoman Empire were distributed to the Allied powers as [[League of Nations mandate]]s. Britain gained control of [[Mandatory Palestine|Palestine]], [[Emirate of Transjordan|Transjordan]], [[Kingdom of Iraq (Mandate administration)|Iraq]], parts of [[British Cameroons|Cameroon]] and [[British Togoland|Togoland]], and [[Tanganyika (territory)|Tanganyika]]. The Dominions themselves acquired mandates of their own: the [[Union of South Africa]] gained South West Africa (modern-day [[Namibia]]), Australia gained [[Territory of New Guinea|New Guinea]], and New Zealand [[Western Samoa Trust Territory|Western Samoa]]. [[History of Nauru#World War I to World War II|Nauru]] was made a combined mandate of Britain and the two Pacific Dominions.{{Sfn|Fox|2008|pp=23–29, 35, 60}}