Some books are much better at this than others. And while I don't believe the bible was that prevalent in the wars of the past, even if it was, that was centuries ago. We've cast aside such foolish things yet live in a world where many people have not.
And that's our problem.
On your second paragraph - that's exactly why an ideology that can transform a person from a citizen into a terrorist because they feel marginalized needs to be addressed. There's a whole lot of marginalized people across our globe.
While it's true that many disfranchised individuals turn extremist it's also true that just as many of those who do are very privileged. People don't decide to join ISIS because they are poor, the do so because they are influenced to do it in a very methodical and well financed way.
But my point is the current terrorist attacks in Paris are committed by people who got discarded by society with no purpose in life and they found a group who gave them a place where they felt needed and respected.
Brevik is a Nazi and he is not Christian