You're wrong about the aztecs actually. They forced smaller tribes in their territory which they conquered to be sacrificed or have their entire tribe destroyed. Thus they had a ready made supply of sacrifices who didn't have a choice if they wanted their families to live. It was this distrust that the spanish used to defeat the aztecs using those dissadent tribes tired of huge tribute and sacrifices as an army and wipe out the aztec civilisation. Just as the tribes were in turn wiped out by diseases carried by the spanish that they wern't immune to like the spannish - thus the land was clear for the main spanish people to move in.
Also don't forget the white mantle stopped the release of the titans and stopped the titans destoying everything.