A world war is a major military conflict that occurs across several continents and involves many countries, both large and small. The first world war was a massive struggle on land, sea and air between more than 50 nations from 1914 to 1918. It is considered the deadliest war in history and involved a larger number of casualties than any other war to date. It was also the first time that a large number of the world’s largest economies, including the United States and the Soviet Union, became fully engaged in a global war.

World War I was triggered by the assassination of Archduke Franz Ferdinand in Serbia on 28 June 1914. The assassination provoked a crisis between the major European powers, with Germany and Austria-Hungary joining forces to form the Triple Alliance and Russia and France creating a separate pact. The United Kingdom remained neutral, but it quickly joined the alliances after the sinking of the passenger ship Lusitania on 7 May 1915.

The conflict quickly expanded beyond Europe, with the colonies of the major powers becoming involved as well. Australia, India, China and New Zealand joined the Allied forces. The war also shifted the balance of power in Asia as Japan began expanding its empire, leading to conflicts with the US and Britain.

In the United States, the government hoped to mobilize support for the war effort through appeals to patriotism and civic duty. Its propaganda compared the enemy to “mad gorillas” and linked US democracy with support for the democracies of Western Europe.