The assassination on 28 June 1914 of Archduke Franz Ferdinand of Austria, the heir to the throne of Austria-Hungary, was the proximate trigger of the war. Long-term causes, such as imperialistic foreign policies of the great powers of Europe, including the German Empire, the Austro-Hungarian Empire, the Ottoman Empire, the Russian Empire, the British Empire, France, and Italy, played a major role. Ferdinand’s assassination by a Yugoslav nationalist resulted in a Habsburg ultimatum against the Kingdom of Serbia. Several alliances formed over the past decades were invoked, so within weeks the major powers were at war; via their colonies, the conflict soon spread around the world.
On 28 July, the conflict opened with the Austro-Hungarian invasion of Serbia, followed by the German invasion of Belgium, Luxembourg and France; and a Russian attack against Germany. After the German march on Paris was brought to a halt, the Western Front settled into a static battle of attrition with a trench line that changed little until 1917. In the East, the Russian army successfully fought against the Austro-Hungarian forces but was forced back by the German army. Additional fronts opened after the Ottoman Empire joined the war in 1914, Italy and Bulgaria in 1915 and Romania in 1916. The Russian Empire collapsed in 1917, and Russia left the war after the October Revolution later that year. After a 1918 German offensive along the western front, United States forces entered the trenches and the Allies drove back the German armies in a series of successful offensives. Germany agreed to a cease-fire on 11 November 1918, later known as Armistice Day.
By the war’s end, four major imperial powers—the German, Russian, Austro-Hungarian and Ottoman Empires—had been militarily and politically defeated and ceased to exist. The successor states of the former two lost a great amount of territory, while the latter two were dismantled entirely. The map of central Europe was redrawn into several smaller states. The League of Nations was formed in the hope of preventing another such conflict. The European nationalism spawned by the war and the breakup of empires, the repercussions of Germany’s defeat and problems with the Treaty of Versailles are generally agreed to be factors in the beginning of World War II.
World War II, or the Second World War (often abbreviated as WWII or WW2), was a global military conflict lasting from 1939 to 1945, which involved most of the world’s nations, including all of the great powers: eventually forming two opposing military alliances, the Allies and the Axis. It was the most widespread war in history, with more than 100 million military personnel mobilised. In a state of “total war,” the major participants placed their entire economic, industrial, and scientific capabilities at the service of the war effort, erasing the distinction between civilian and military resources. Marked by significant events involving the mass death of civilians, including the Holocaust and the only use of nuclear weapons in warfare, it was the deadliest conflict in human history, resulting in 50 million to over 70 million fatalities.
The war is generally accepted to have begun on 1 September 1939, with the invasion of Poland by Germany, and subsequent declarations of war on Germany by France and most of the countries of the British Empire and Commonwealth. Germany set out to establish a large empire in Europe. From late 1939 to early 1941, in a series of campaigns and treaties, Germany conquered or subdued much of continental Europe; amid Nazi-Soviet agreements, the nominally neutral Soviet Union fully or partially occupied and annexed territories of its six European neighbours. Britain and the Commonwealth remained the only major force continuing the fight against the Axis in North Africa and in extensive naval warfare. In June 1941, the European Axis launched an invasion of the Soviet Union, giving a start to the largest land theatre of war in history, which, from that moment on, tied down the major part of the Axis military power. In December 1941, Japan, which had been at war with China since 1937, and aimed to dominate Asia, attacked the United States and European possessions in the Pacific Ocean, quickly conquering much of the region.
The Axis advance was stopped in 1942 after the defeat of Japan in a series of naval battles and after defeats of European Axis troops in North Africa and, decisively, at Stalingrad. In 1943, with a series of German defeats in Eastern Europe, the Allied invasion of Fascist Italy, and American victories in the Pacific, the Axis lost the initiative and undertook strategic retreat on all fronts. In 1944, the Western Allies invaded France, while the Soviet Union regained all territorial losses and invaded Germany and its allies.
The war in Europe ended with the capture of Berlin by Soviet and Polish troops and the subsequent German unconditional surrender on 8 May 1945. The Japanese Navy was defeated by the United States, and invasion of the Japanese Archipelago (“Home Islands”) became imminent. The war in Asia ended on 15 August 1945 when Japan agreed to surrender.
The war ended with the total victory of the Allies over Germany and Japan in 1945. World War II altered the political alignment and social structure of the world. The United Nations (UN) was established to foster international cooperation and prevent future conflicts. The Soviet Union and the United States emerged as rival superpowers, setting the stage for the Cold War, which lasted for the next 46 years. Meanwhile, the influence of European great powers started to decline, while the decolonisation of Asia and Africa began. Most countries whose industries had been damaged moved towards economic recovery. Political integration, especially in Europe, emerged as an effort to stabilise postwar relations.