Why were Aztec Empire defeated?

I look at the Spanish invasion in two parts. The first part took place from 1519 to 1531 where the Spaniards defeated the Aztec Empire and other nations within Anawak with their steel, guns and germs. The second part the Spaniards launched the genocide of the mind campaign, which converted the Mexikah people and other peoples to Catholics. Also, lets not forget that once the Mexikah people started learning the spanish language they also started forgetting their native language Nahuatl.