The warriors didn't earn more power, wealth, or land. The people who started the wars did, but what do you think was the motivation of the people on the field? Religion is a form of mind control. It's the opiate of the masses. A way to explain what can't be explained. "Moral support" is a byproduct, not a purpose.
I don't think religion was the motivating factor of most soldiers (including Islamist extremists). Some were forced into service, Roman soldiers were promised cash and a plot of land, free clothing and annual pay, see the world, protect the homeland (patriotic reasons), learn a skill, lack of other careers, plunder. Probably a lot of the same reasons soldiers join today.
I don't remember that much about the Crusades but I remember reading about Crusaders killing fellow Christians to gain power and riches. Certainly the Pope played a role but his power was not limited to religion. Religion probably played a larger role for many in the Crusades, but world history is full of armies and conquests.
I remember reading a book about Lawrence of Arabia. He would plan some campaigns with important military targets but the Arabs would change those to other cities where the looting was better.
ok. fucking loser.