I know of all the Latino-Americans who have been in the U.S. for hundreds of years. My question is regarding the populations (for the sake of the rule, as of 2002) of America and Mexico. One is primarily mestizo--indigenous, white, and some black. The other is primarily white with some black. But specifically, the population of Mexico is more mestizo than America, which is majority white. Why did America not have more mestizo (indigenous + white (+some black)) population, especially compared to Mexico, which is primarily mestizo?

Obligatory race is merely a social construct. I'm just interested in how two regions (current U.S. and current Mexico) have such disproportionately different percentages of mestizos (U.S. has more white).