World war is the name given to a series of conflicts that occurred between nations from 1914-1945. The conflicts were triggered by a number of events that led to escalating political tensions and wars of aggression.
Among other things, the war started because of the assassination of Archduke Franz Ferdinand of Austria in Serbia on 28 June 1914. This event quickly invoked a number of alliances that the European powers had formed in recent decades.
The conflict spread from Europe to Africa and into the Indian Ocean region and Asia. It was a war of colonial empires as well as a war of ideas.
Many of the European colonies were in danger of collapse. The British and French were especially vulnerable.
African revolts grew to challenge the authority of European colonial regimes in places like southern Ivory Coast, Libya and Karamoja in Uganda. These revolts forced the Allied powers to divert their scarce military resources needed for fighting the Germans on the Western Front to dealing with local revolts.
The people of Russia also began to rebel against their tsar, and their revolution began in March 1917. The German army, recognizing the growing popularity of the revolutionary movement in Russia, made plans to send an exiled Marxist named Vladimir Lenin across Europe and back into Russia.
The United States, under President Woodrow Wilson, fought against Germany and Austria-Hungary. In addition to its naval blockade of German shipping destined for Britain, the United States tightened an economic blockade of Japan which threatened Japanese oil supplies.