I am sorry if this question has been answered before but I am genuinely curious. It looks like the U.S. didn't really have a dog in the fight on top of having a large German population. What made them go from fighting the British 100 years earlier to joining their side?
There is a good deal more to say, but, while you wait for fresh responses to your query, you might like to review these two earlier responses, which both address German provocations which helped to push the US into the Allied camp:
The Zimmerman telegram, which attempted to persuade Mexico to attack the US
The Lusitania, a merchant ship carrying many Americans, sunk by a German U-boat, and the Black Tom explosion – an American munitions factory destroyed by German espionage. (And see the U-boat campaigns of 1914-17 more generally.)