Which event bring the united states into world war 1

The German subs were attacking the American subs

Most definitively, the event that actually caused the US to be brought into the war was the Zimmerman Telegram. The Zimmerman Telegram was a secret transmission to Mexico from Germany. It was intercepted by Britain, and shown to the US. It requested that Mexico attack the US if the US entered the war on the side of the Allies. This telegram infuriated America, and thus, brought a declaration of war upon Germany.