World War I opens with two bullets in Sarajevo, the 1914 assassination of Archduke Franz Ferdinand and his wife Sophie, and traces how that killing pulled Austria-Hungary, Russia, Germany, and Britain into a war Americans initially watched from a distance. Narrator David Carradine follows the chain of events that ended American neutrality: German submarines sinking US cargo ships, and British codebreakers intercepting the Zimmermann telegram proposing a German-Mexican alliance, which pushed the United States to declare war on April 6, 1917. The film puts faces on the American war effort, Charles Whittlesey and the men of the Lost Battalion, Father Duffy of the Fighting 69th, pilot Victor Chapman, Quentin Roosevelt, and ambulance driver Richard Hall among them, some surviving against long odds and others killed in action. It tallies the war's toll bluntly: 14 million dead, roughly $190 billion spent, and, by the film's count, three men wounded or driven mad for every one killed. The film closes by tracing that legacy into the monuments and social changes still visible in American life today.