There was no one single cause for the World War I. Many different factors led to the conflict, including the growth of Germany’s army and its industrialization plans. As a result, major military alliances were formed between countries to protect their interests. Germany, Austria-Hungary, France, and Russia signed agreements that would ultimately lead to the conflict. The Allies and Central Powers were a part of the alliance, but the United States joined in 1917, adding its own men and materiel to the fray.

The war ended in 1945 when the Allies defeated the German, Austria-Hungarian, and Ottoman empires. The League of Nations was created to prevent another conflict, and the Soviet Union became a rival superpower. In the aftermath of the war, the United States and the Soviet Union established themselves as the two superpowers, amidst the devastation. The war also brought Western democracies into conflict with the Soviet Union, a country that had fought against the United States during the First World War.

Germany declared war on the United States on 11 December 1941. The Soviet Union, meanwhile, made a remarkable recovery. A huge Soviet encirclement in November 1941 cut off the Germans from advancing to their goal of the Soviet Union. The battle of Alamein, a predominantly Italian force, was won by Montgomery in November 1942. Between 1942 and 1945, the United States and its allies fought mostly a naval war, using their vast naval strength in major amphibious operations. The TORCH operation combined American and British troops.