I think that religion is the reason that’s often used to mask simpler motives; people want other people’s stuff–their land, their wealth, their resources–without having to expend work to get it themselves. Or perhaps they can’t get what they want/need without taking it from their neighbors. For instance, Japan is a very small country, and seriously lacks natural resources; in order to compete internationally, they needed to become an expansionist empire in the late 1800s/early 1900s, which led to them bombing Pearl Harbor in order to attempt to stop our imperial ambitions in the Pacific. Sure, Japan made claims about the emperor being divine, but it was fundamentally about resources.