It seems to me when you look at ancient religions, they mostly function as ways of hardening tribalism. Ancient religions did not really ever say “your gods are not real.” They said, “your gods are inferior.” This fact is sometimes used to prove the greater perniciousness of Christianity, since it drove Christianity to proselytize others, and this is a great evil, to the modern mind. The ancient pagans did not often try to proselytize the followers of other gods. But the forcible conversion of unbelievers is no part of Biblical Christianity and happened more rarely than most people seem to think. On the other hand, when you say, “your gods are inferior,” given the way religion worked in ancient times as an inseparable aspect of a particular ethnic group’s culture, what you were actually saying was, “you are inferior.” The inferiority of another people was justification for attacking and enslaving them. And how did you know they are inferior? Because you were able to attack and enslave them. If their gods were stronger than your gods, they would have protected their people from you. So yes, they didn’t proselytize followers of other gods, but they did attack and enslave them all the time.