Answer:
One factor was unrestricted submarine warfare on U.S. civilian ships. And our factory of making big things like ships.
Another thing was because of Britain used to have the greatest Navy. And we made ships for them.
And one last things was the Zimmerman telegram in which Germany tried to ally with Mexico against the USA. Also that's how we got Texas and New Mexico, was because it used to be runned by Mexico.
Step-by-step explanation:
That's why the U.S. to join allies. I explained within the answer.