Why did US join first world war?

The sinking of the Lusitania and sinking of American vessels. Also a telegram (no one knows if it is was real of fake) was sent from the British Empire to America, stating that they intercepted it from the Germans. The telegram read, "Mexico, if you join the axis powers you can have all the land you want in the United States,".

Of course no one knows if that is true or not.