The introduction of Buddhism to Japan between the 6th and 8th c. over the pre-existing practices (shintoism / proto shintoism) caused a few civil wars between the clans trying to push the royal family one way or the other and convert the whole country. Very political - control religion, control the king, control riches, control the country. Very bloody. Buddhism won with the usual secret ingredient, genocide (well, of clans, not entire ethnicities, but still basically).
Mesopotamia had lots of wars that had the gods of each involved city in their backdrop, but most of the time that was more of an excuse and not primarily a religious war. You did have a bunch of kings declaring “my god ordered this war, I am nothing more than the executor of his will” on their victory steles in the Early Dynastic period (around 3000 to 2300 BCE), but religious practices were pretty much not involved at all in those conflicts, it was exclusively about taking grain and land.
The introduction of Buddhism to Japan between the 6th and 8th c. over the pre-existing practices (shintoism / proto shintoism) caused a few civil wars between the clans trying to push the royal family one way or the other and convert the whole country. Very political - control religion, control the king, control riches, control the country. Very bloody. Buddhism won with the usual secret ingredient, genocide (well, of clans, not entire ethnicities, but still basically).
Mesopotamia had lots of wars that had the gods of each involved city in their backdrop, but most of the time that was more of an excuse and not primarily a religious war. You did have a bunch of kings declaring “my god ordered this war, I am nothing more than the executor of his will” on their victory steles in the Early Dynastic period (around 3000 to 2300 BCE), but religious practices were pretty much not involved at all in those conflicts, it was exclusively about taking grain and land.