It began after the assassination of Archduke Franz Ferdinand by Serbian nationalist Gavrio Principe, which would set off the chain of events that lead each nation of Germany, Russia, and the Austria-Hungarian empire to battle against the British, French, and American forces for four long and grueling years from 1914 to 1918.
The US involvement came into play after many different factors, from the German U-Boats sinking American freight vessels, to the Zimmermann Telegram. All of which were catapults leading up to the need from England to ask America for assistance during the war as the British were also being heavily taken out by the Germans as well.
