someone of a different belief system is a very convenient bogeyman for the hawks in all modern governments
This couldn’t be more true.
It’s a lot easier to build public support for killing people and destroying their countries if you can convince that public that the people your killing are irrational, unreasonable nutjobs that should be feared. Focus on the differences and dehumanise them as far as possible.
It doesn’t need religion to stir this up – it comes just as easilly from an intolerance, fear or hatred of the other side’s religion or culture.
So it’s not always people who “want more power” that start war, it’s “people who want more power and can gain mass support from their citizens by using religion as the easiest justification”
It does happen, but is a bit over-simplistic. Modern wars are as likely to be motivated by a desire to destabilise, disrupt or destroy a potential rivals power base, often without a desire to replace them and take that power over. And any ideology can be used, political or economic as easily as religious.