For a brief moment I am going to take off my troll hat and put on my historian robe.
As Uzi said, each religion developed in a different context. For Christianity, it arose during a period of Roman occupation of Palestine and after a failed Jewish rebellion where the Jews were punished pretty harshly. Nietzsche's theory on Christianity is that many of its values were created out of resentment for Roman values. The whole master-slave thing went into how Roman values were life affirming and celebratory while Christians cherished meekness. Any way, after the death of Jesus, his apostles spread throughout the Roman empire and preached Christianity. It became popular with the various people who also subjects of Rome. In the bible, it goes into how the early non-Jewish adopters of Christianity weren't interested in Jewish customs like circumcision and not eating pork so it was agreed upon that Christians didn't have to follow Jewish customary law. Christianity spread and eventually and what we know as the bible was compiled and edited for a few hundred years after the death of Jesus.
What does this have to do with Islam being a violent religion?Mohammed used Islam to unify the various Arab tribes. At the time of his death, the East Roman Empire, and Persian empire (I am not looking up how to spell their specific names), had just concluded a 30 year long war with each other. Many Arabs returned to Arabia after serving as mercenaries for those empires. The demographics of Arabia combined with the depopulated middle east meant that Arab tribes and armies were going to stomp through the middle east in some form or another to the detriment of Christians, Jews, and others already there. It was Omar, Mohammad's immediate successor and a former warrior, who started the conquest of non-Arab land.
The Koran was compiled while Mohammad was alive. That is where a lot of Sharia is extrapolated from. But the secondary and much larger group of sources is the hadith which was compiled hundreds of years after the death of Mohammed by scholars working for the Arabian successor empires. A lot of the hadith is sayings and people mentioning seeing things. Most are innocuous like
The Prophet in his fatal illness, called his daughter Fatima and told her a secret because of which she started weeping. Then he called her and told her another secret, and she started laughing. When I asked her about that, she replied, "The Prophet told me that he would die in his fatal illness, and so I wept, but then he secretly told me that from amongst his family, I would be the first to join him, and so I laughed."
So much of what people think Islam is and sharia itself isn't derived directly from Mohammad, the same way a lot of Christian law and ideology didn't come from Jesus.
I will link this to ISIS and modern times a little later today if anyone cares.
