World wars
First World War
Britain entered World War I with Herbert Henry Asquith of the Liberal Party as Prime Minister. Asquith declared war on the German Empire on August 4, 1914, in response to demands for military passage forced into Belgium by Germany, and the completion of Britain's own ultimatum that day. Britain's reasons for declaring war were complex: the London treaty had committed the United Kingdom to safeguarding Belgium's neutrality in the invasion,
but the office of the Ministry of Foreign Affairs and the Commonwealth of Nations had concluded that the treaty might not comply with. Long and secret meetings regarding Britain's moral commitment took place from 1905, but many of Asquith's cabinet members were unaware of them until 1911.2 The state's armed forces were reorganized and the size of the armed forces increased. Armed Forces, due to the introduction of forced enlistment in 1916, for the first time in the history of the United Kingdom. The British royal family, under George V of the United Kingdom, dissolved relations with their German cousins and changed their Germanic name "House of Saxe-Coburg-Gotha" to the distinguished English "House of Windsor".
The Second World War
Britain, along with its dominions and the rest of the Empire, declared war on Nazi Germany in 1939, after the German invasion of Poland. After the lull of the "fake war", the French and British armies collapsed under German attack in the spring of 1940. The British rescued their army at Dunkirk, leaving all their war equipment and supplies behind. Winston Churchill came to power, promising to fight the Germans to the end. First, the Germans tried to achieve air supremacy, but were defeated by the Royal Air Force in the Battle of Britain in late summer 1940. Japan declared war in December 1941, and quickly seized Hong Kong, Malaysia, Singapore and Burma, and threatened Australia and India. Britain formed an alliance with the Soviet Union and very close ties with the United States.