Respuesta :
The alliance with Mexico, however an even bigger reason is when German U boats sank the Lusitania which had on board several US citizens.
A - Germany made a secret offer to Mexico to form an alliance to fight the United States.
This greatly enraged at the time neutral US. For that reason (and also for a couple of other reasons) the United States decided they would declare war on Germany and enter the Great War, as it was called at the time.
This greatly enraged at the time neutral US. For that reason (and also for a couple of other reasons) the United States decided they would declare war on Germany and enter the Great War, as it was called at the time.