Humans will always form tribes and groups, and pretend that their way is better than “those guys”. The motive for almost every single war is power and resources, not theology. People just use religion, or any other excuse, to justify war.
This means that you can’t blame wars for being “secular”, almost every war is. That would be like calling any other colour, “not black”. It’s idiotic. This also means that you can’t say that religion is the cause of so many wars because you can bet that if religion didn’t exist, some other excuse would be used to wage said wars.