What caused the United States to join the Allies in fighting World War 1?
the Germans' use of unrestricted submarine warfare
the Germans blocked the U.S's trade route with Britain and blew up out ships every time we came near the British isle to trade goods. the British also blocked off the way to the German ports with underwater explosives. so once the Germans blew up the Lusitania, the Americans were angered and pushed to the edge in which we joined the war on the Allies side, not the central powers