“1. When was the last time Mexico threatened the USA with a war?”
The Mexicans were in contact with the Third Riech before 1941.
I hope we don’t have to kick their ass again. We can’t afford another Marshall plan.
5.56mm
The Mexicans were in contact with the Germans in WW1, too.
Look up Zimmerman Telegram: a bit of U.S. cryptography that provided the smoking gun to bring America into the war.