When you meet those who are infidels, strike their necks until you have overwhelmed them, tighten their bonds, and then release them, either freely or for ransom, when war lays down its burdens. Thus it is, and if God wished, he would crush them Himself, but he tests you against one another. Those who are killed in the path of God, He does not let their good deeds go for nothing. - The Qur'an
The war against the infidel is as holy to the warriors of Islam as the Crusades are for Christian knights. Both fight in defense of their religions and because of this, both fight with the sure knowledge that by their actions they are assured of the salvation of their souls and entry into Paradise. Whatever they do, in the name of God, is just, for they fight for the honor and glory of a just and merciful God. The wars between Islam and Christianity are among the most bloody and brutal ever recorded.