you take an in depth look of those events, there were always inherent political and economical motives. Explicitly saying that you want to assert authority, consolidate power, and acquire more land and wealth by slaughtering bunch of innocent people sounds awful, doesn’t it?

And those leaders have used (organized) religion to control the masses such that said political leaders could do exactly that. More over, consider that until the rise of Christianity, Islam and Buddhism, most relations were distinctly national. Even the Israelites used their particular deity to justify genocide (Invasion of Palestine, Cannan, and the rest of that corner of the world, the biblical narrative places as they entered the promised land). Babylonians and Egyptions and Greeks and Romans all used their patron gods to excuse invasions. As did buddhists and muslim leaders. (even if buddhism might technically be an atheist religion.)

Saying that most wars are caused by religion seems like a stretch, considering conflicts have existed long before human even existed and fights are going to happen anyway. I’m not sure if that’s any worse than invading Iraq for “freedom” or Stalin and Mao killing their people because they were “counter-revolutionaries”

Understand that the first evidence of religion also predates modern humans, with graves found with neanderthals in them.

Stalin and Mao are only VERY recent in human history. As is, obviously, the second iraq war (and american patriotism might be seen as it's own kind of religion. Terrifying that.). and for most of human history, religion has been the predominate tool for social control. In point of fact, it still is. and for the bulk of that, clergy have tied their authority on to the king. Divine Right of Kings being justification for why they get to bully people around (because god said they could.) even after the idea that the church and state should be separate occured to St Augustine... (incidentally first elaborated on in a book intended to explain that the Visigoth's sacking rome had nothing to do with roman conversion to christianity...) it was always intended as a defense of the church's authority from being encroached... and never the other way 'round. it wasn't until Luther did his thing (and hey, look, more wars,) that we got our modern conception of separated church and state. (my understanding of similarities, the buddha never encouraged anyone to be involved in politics... but then Ashoka happened... see my comment about organized religion always being used for social control.)

in most of human history... organized religions were nationalized into supporting local leadership. They had their own national diety, and the military successes were always a result of their diety being stronger than others, as well as maybe other natural disasters happening (like maybe the bubonic plague hitting palestine when the ark of the covenant was held in Dagon's temple. you see similar assertions of divine intervention in the wars between greek city states, and with the south american empires.)

that the leaders in those religions were greedy bastards with ulterior motives is not particularly surprising, but not particularly relevant. Throughout most of human history, the religious and secular were inextricably linked, with religion being used to control the commoners and justifying what would be- as you note- an otherwise unjustifiable war. The clergy allowed this so they themselves could maintain their own power, wealth, and status in their society; and the rulers allowed it because the clergy allowed them to be assholes. it was fear of divine retribution that kept people in line.