World War I began in Europe with the assassination of Archduke Franz Ferdinand of Austria on a visit to Sarajevo, Bosnia. the united states entered the war on April 6, 1917 as result of Germany's policy of unrestricted submarine warfare which violated its neutrality. the failed final German offensive of march 21, 1918 timed to occur before significant American forces could arrive, resulted in the abdication of the Kaiser and Germany being forced to sue for peace. The battles of Chateau-Thierry, Belleau wood and the Meuse-Argonne were primary sites of the American fighting.