Did Cortez have anything to do with that?
How did you find a 5-year old post?
When the Spanish came they inadvertently brought a lot of Old world diseases that killed off the inhabitants well before Spanish steel came into play. As an aside, the germs spread out well before Europeans -- in Mississippi the cities there were contacted by tribes who met other tribes who had met one Spaniard, but smallpox, etc spread and people died like flies
Males also are far more susceptible to diseases than females, so far fewer men due to disease and then fewer still due to war.
the Spaniards mostly sent across men, who intermarried or otherwise slept with local woman. That's why Mexicans are mainly European today -- except in the deep south where you may find a full blooded Mayan