The Spanish invasion was not a meeting of equals, where each side could try to convert the other. The Spanish generally had overwhelming military power. More importantly, they had magic that must have come from the gods (especially guns), and even looked like the gods. When the Spanish told the Aztecs to believe in Jesus, there was no debate and rarely any resistance - the Aztec people accepted the teachings of the Spanish.
Who attacked other religions and tried to convert others the Spanish or the Aztecs ?
The spanish were christian, and the Aztecs were Mexicayotal. The spanish tried to convert the Aztecs.
The Spanish enslaved the Indians and threatened them with death if they did not convert to Christianity. The Indians converted for self preservation.
The Spanish had guns and the Aztecs did not.
the spanish thought of the aztecs as slaves
Christianity
The Spanish were very wary of the Aztec religion. In some cases they even exploited it. Perhaps most importantly though, their attitude showed that they did not like the Aztec religion and tried to convert the Aztecs to Christianity.
Yes the Aztecs welcomed the spanish with gifts
the Spanish gave small pox to the Aztecs.
The technology of the Spanish greatly exceeded the Aztecs. The Spanish were shooting bullets, the Aztecs were throwing stones, no contest.
The Aztecs had gold.
The Spanish conquest of the Aztecs was due to the fact that the Aztecs at first did not realize that the Spanish were going to try to conquer them. Even when they did, the Spaniards had superior weapons and the Aztecs were unable to defeat them.