British entry into World War I

Decision for war

After British leaders increasingly had a sense of commitment to defending France against Germany – first if Germany again conquered France, it would become a major threat to British economic, political and cultural interests. Secondly, partisanship was involved. The Liberal Party was identified with internationalism and free trade, and opposition to jingoism and warfare. By contrast the Conservative Party was identified as the party of nationalism and patriotism; Britons expected it "to show capacity in running a war." Liberal voters demanded peace, but they also were outraged when the Germans treated Belgian neutrality as a worthless "scrap of paper" (in the words of the German chancellor ridiculing the Treaty of London (1839)). Germany invaded Belgium en route to a massive attack on France early on the morning of 4 August. The victims called upon Britain for military rescue under the 1839 treaty and in response, Britain declared war on Germany that same evening. As late as August 1, 1914, the great majority of Liberal--both voters and cabinet members--strongly opposed going to war. The German invasion of Belgium was such an outrageous violation of international rights that they voted for war on August 4. Unless the Liberal government acted decisively against the German invasion, its top leaders Including Prime Minister H.H. Asquith, Foreign Minister Edward Grey, navy minister Winston Churchill and others would resign, leading to control of the British government by the much more pro-war Conservative Party. Mistreatment of Belgium itself was not a main cause British entry, but it was a main justification used extensively in wartime propaganda to motivate the British people.

Canadian Army recruitment poster

The German high command was aware that entering Belgium would trigger British intervention but decided the risk was acceptable; they expected it to be a short war while their ambassador in London claimed civil war in Ireland would prevent Britain from assisting France.

The declaration of war automatically involved all dominions and colonies and protectorates of the British Empire, many of whom made significant contributions to the Allied war effort, both in the provision of troops and civilian labourers.