Answer:
I would say into WW1 because of the Zimmerman affair.
Explanation:
United States entered the WW1 in 1917, although for three years they were not officially involved in it. But, then a telegram was intercepted, in which an official letter was sent to Mexico by German authorities.
According to it, Mexico was to declare war on United States, while Germany will support them in the war efforts.
Many historians are doubting the reliability of this document.
