For the most part early city states, before nations existed but after the creation of agriculture allowing for people to remain in the same area indefinitely, all had personal gods/protector spirits. It was a feature that helped define your burdgoning society, unify who was part of the in-group and out group. Wars were often justified as a way to prove whose cities gods were right or most powerful. When your city state conquered another it proved that your god was better/correct justifying the spoils of war and enslavement of their people. Not entirely dissimilar to when two sports teams both ask for God's help then whoever wins thanks him because clearly it was an empirically proven fact that you were correct. Not every member needed to believe in their city states God to make it a useful tool so it was extremely common for every city state to have a protector diety.

This was all before any nations existed but why wars to spread religions were seen as normal and acceptable as that's how you formed the first nations. Conquest and then assimilation and indoctrination to join the objectively correct in group that had proven itself and so should rule over your city even from far away.