Un-restricted submarine warfare. If it wasn't for that, the US would not have entered the war. As it was, the US was only in it for a year anyway...it ended in 1918 (the US entered the war in 1917).
do you mean what caused us entry into world war one? if so then the sinking of the USS Lusitania by German u-boats was what caused American entry into the war
The US became a combatant, part of the allies in 1917.
1909 to 1944 The US entered World War 2 in December of 1941.
Japanese attack at Pearl Harbour. That's World War 2. The United States entered World War I after the Zimmermann note, which offered German aid for a Mexican invasion of the US, was intercepted, translated and sent to Woodrow Wilson by the British.
Militarism, the other three causes for US entry into the war are imperialism nationalism and alliances.
Communist aggression.
The Franco-Prussian War was not directly related to the entry of the US into World War I.
Gen. John J. Pershinghttp://en.wikipedia.org/wiki/John_J._Pershing
The Japanese sneak attack on Pearl Harbor propelled the US into the war.
the entry of US troops.
mr
Entry into the war caused it to end more quickly