What if their reasons are:And the underlying cause of a conflict between Civilisation A and Civilisation B is....Power, one civilisation seeking dominion over the other using their religion as the justifying factor...the cause is not the religion itself, but the need for dominion and power manifested through religion. We see similar conflicts justified by ideology and politics...some of the major conflicts in our history have been justified by the spread of Democracy or Communism..when the underlying factor is ultimately control and power.
"But my god told me to, I am helping them, we don't want control or power over them we just want them to follow the one, true religion, their religion isn't true, it's lies, honest, ask my priest"
Can you not see how religion is people taking things that aren't one hundred percent true, interpretable at best and passing them on as fact and as being the one true way of life.
Again I go back to is it: cause A's conflict being justified by religion or religion's conflict being justified by cause A.
Wars of conflict and power are a lot more concrete, "we want what you have and we're going to take it".
Wars of religion are not so concrete, "What I believe is correct, what you believe in isn't correct, we will make you believe".
Few wars are that simple.
I do doubt any war has ever been that simple, however it has been a major factor in a lot of wars.