Political integration, especially in Europe, emerged as an effort to end pre-war enmities and to create a common identity.
beginning with the German invasion of Poland; Britain and France declared war on Germany two days later. Taylor, who held that the Sino-Japanese War and war in Europe and its colonies occurred simultaneously and the two wars merged in 1941. Other starting dates sometimes used for World War II include the Italian invasion of Abyssinia on 3 October 1935.
On 22 June 1941, the European Axis powers launched an invasion of the Soviet Union, opening the largest land theatre of war in history, which trapped the major part of the Axis military forces into a war of attrition.
In December 1941, Japan attacked the United States and European colonies in the Pacific Ocean, and quickly conquered much of the Western Pacific.
From 1922 to 1925, the Fascist movement led by Benito Mussolini seized power in Italy with a nationalist, totalitarian, and class collaborationist agenda that abolished representative democracy, repressed socialist, left-wing and liberal forces, and pursued an aggressive expansionist foreign policy aimed at making Italy a world power, promising the creation of a "New Roman Empire".Meanwhile, the victorious Allies of World War I, such as France, Belgium, Italy, Romania and Greece, gained territory, and new nation-states were created out of the collapse of Austria-Hungary and the Ottoman and Russian Empires.To prevent a future world war, the League of Nations was created during the 1919 Paris Peace Conference.With an invasion of the Japanese archipelago imminent, the possibility of additional atomic bombings and the Soviet invasion of Manchuria, Japan formally surrendered on 2 September 1945.Thus ended the war in Asia, cementing the total victory of the Allies.The Axis advance halted in 1942 when Japan lost the critical Battle of Midway, and Germany and Italy were defeated in North Africa and then, decisively, at Stalingrad in the Soviet Union.In 1943, with a series of German defeats on the Eastern Front, the Allied invasion of Sicily and the Allied invasion of Italy which brought about Italian surrender, and Allied victories in the Pacific, the Axis lost the initiative and undertook strategic retreat on all fronts.World War II was the deadliest conflict in human history, marked by 50 to 85 million fatalities, most of which were civilians in the Soviet Union and China.It included massacres, the genocide of the Holocaust, strategic bombing, starvation, disease, and the first use of nuclear weapons in history.The German Empire was dissolved in the German Revolution of 1918–1919, and a democratic government, later known as the Weimar Republic, was created.The interwar period saw strife between supporters of the new republic and hardline opponents on both the right and left.