To the best of my understanding, Islam is an amalgam of Judaism and Christianity, developing at a time and place of conflict between the two. As we know, Christianity grew out of Judaism a mere six hundred years earlier. All three Abrahamic religions believe in a special relationship with God/Allah/Jesus resulting in inner peace and blessings, both in the present life and in the hereafter. Their sacred texts, interpreted by divinely inspired leaders, instruct them on dealing with enemies in the physical and spiritual worlds. Throughout the centuries and millennia this has often manifested in armed conflict from all sides.
All the Muslims I know are good, kind, peaceful people—good Christians, as some would say except they might take offence at being called “Christian” when they are, in fact, “Muslim.” Muslims and Christians have been at war since the first Muslim started this new religion called Islam back around 600 AD/CE. The Christian Crusaders marched on the “infidel,” that is the Muslims, to “take back” land that Christians believed belonged to them as a spiritual heritage. This included Jerusalem.