Wars are fought because of access to resources. Whatever the public reasons given are, God, King, Country, Volk, etc. are just marketing ploys to get people to support the effort.
I’d probably put it more broadly that wars are fundamentally about economics, but yes, other than that, the rest is just packaging to get able-bodied men to run off and slaughter and be slaughtered.
Look at the Crusades. Sure, there was some great desire to save Christianity in its birthplace, but the reality was that Anatolia and Palestine represented the most important trade corridor in the Old World; the meeting place of three continents, and whomever controlled could make a fortune off of the goods moving back and forth across the trade routes. So sure, let’s save Jerusalem and Bethlehem and those mildly schismatic Eastern Christians, oh yes, and let’s found Crusader kingdoms as well!
I honestly doubt there’s ever been a war, even a so-called religious war like the Thirty Years War, which really was about religion at all. Religion was simply a placemarker; a bit of good old-fashioned tribalism. That’s not to say there weren’t religious elements; you can’t deny that the Thirty Years War was the inevitable culmination of tensions between Protestants and Catholics in the Holy Roman Empire and surrounding areas, but those tensions were hardly limited to theological disagreements.
In fact, I’d go further and say the Reformation itself was fundamentally economic and political in nature; that a number of Central and Northern European princes had long bristled under what they viewed as the overbearing political power of Rome, and when Martin Luther nailed his 95 Theses on to the door of Wittenberg Castle, they found the opening that poor old Henry IV never had available to him, and kicked it open. “Why Rome has no business telling us who the bishops can be, and in fact, we reject the whole notion that Rome is even the true and proper Church at all! Thanks for all the churches and treasure!”