Presumably the government of Mexico. That in absentia, whomever is attacking and whomever is defending (hopefully any allies Mexico might have).
It would be carried by the United States Northern Command, which oversees most of North America, including Canada, the United States itself, and Mexico.
The president of Mexico, the other command would depend who Mexico was at war with
It would be under the Northern Command.
northern command
Northern
A war in Mexico would be under the command of the military chief of staff of Mexico with the President as Commander in Chief. The military process in Mexico is quite similar to the system in the US.
northern command
A war in Mexico, Central America, or South America would be under the control of the US Southern Command.
The Greeks/Spartans were under command of the spartan Spartucus, and the Trojans were under the command of Paris of Rome.
a fleet
Yes, they should have if it weren't for aussies we would all be ruleing under the command of germany.
Well the most famous war with Mexico was to get the land of what is now Texas. So if we didn't have that war with Mexico there would be no Texas.
1848. US troops under General "Blackjack" Pershing chased Poncho Villa into Mexico in 1916, but that was not a war "with" or "against" Mexico.
Jews were relocated under Hitler's command throughout the war.
Mexico lost much of its territory. Taxes were lowered which were high under the Mexican government.
1971
A provocation to start a war, as Mexico had already warned the US that annexation would mean war (it did; and Mexico lost).