Theologies always take on different forms as they age away from their purist ancient establishment. Those days Islam was great, much like how Sparta was great. It was never just a basic religion. They sought perfection, to develop profound character based upon virtues and principles. There were empires and caliphates rooted in bloodlines. They were not just barbaric desert people running around killing, they were heavily regimented and disciplined in servitude, not to a state, but to a God. Where not praying five times a day was not heard of, where the worship of God was apart of everything that they did, every act, every word, every intention, every thought and every understanding.
At a time of war, it was encouraged to sign a treaty of peace above all else, as war was considered a lack of advancement in the pursuit of perfection. When peace treaties were broken, and there were no choice left other than defense, even then it was forbidden to transgress the boundaries. They had to fight by the will of God, meaning that if they get personally involved (killing somebody out of anger) then they were considered no better than the person they are fighting, they would have fallen out of the remembrance of God, if you like..
similarly, you were not even allowed damage a single tree during warfare. If the enemy put their weapons down, then it was obligated upon you to put your weapon down or else you have transgressed, if you have taken a hostage it was obligated to escort them to a place of safety, feed them and protect them until warfare had ended then release them, or else you have transgressed. Even when it came to killing the enemy on the battlegrounds who refuses to put his weapon down, then you had to kill them quickly without causing much suffering and pain, this is why the sharping/sharpness of the swords were heavily focused upon because of the compassion displayed. Even in the way the killing was executed was of a swift beheading, not the way you would see ISIS do it, slow and painful, but much like how Saudi executes its criminals, it's a split painless second, far less harsh than hanging, electric chair, lethal injection etc.. Bombs and explosions are forbidden, only God is allowed to use fire as means of destruction (hell fire)...
Basically, the focus was always upon on mercy and compassion towards everything and the worship of God being the central point of it all...
Well, i guess..it just isn't like that anymore now...where, in places, there is no mercy or compassion displayed..and in other places where it is, there is no discipline to it..where it becomes self destructive..
This is the time of cowardice. Had humans been less technologically equipped, it would have them all think twice about war, as there is an increased likelihood of their own death...now they can just shoot from a distance.. it really does expose the nature of the human.