It wasn't they who started the fire, it was the enemy. The Axis powers burned civilization upon a pyre, not the Allies. If a good people who hate war are forced to finally fight, they will often fight with dead set anger. It is not the cause of vengeance that they serve, no, it is righteous ire.
They fight for the truth. They will fight to the end. with fires raging, and the innocent dying. For to turn away from duty the world they love will pass, pass forever from view. One after another, like dominoes they fall, but united, they can survive, they will be renewed.