What countries fought in the mexican war?

Answer 1

It would depend on which Mexico war, because Mexico has fought dozens of wars since it became an independent country.

The most known to Americans is the Mexican-American War (1846-1848), when Mexico lost and was forced to surrender most of the present U.S.-Southwest.

Answer 2

The Mexican War was a territorial war fought entirely between the US and Mexico. No other countries became officially involved.