1,001 Sayings and Deeds of the Prophet
Muhammad started it, the war to rid the world of all who refused to submit to the Will of God, as he understood it, after escaping to Medina. As an enticement to kill until none was left who did not accept Islam as his or her religion, after consulting with his Mentor, he announced that the possessions of an unbeliever, including his wives and daughters, belonged to the Muslim who killed him, or absconded with his property.
His strategy was successful and in a few short years the entire Arab population of the Peninsula had converted to Islam or had been killed or taken into slavery. This overwhelming victory over the unbelievers was quickly followed, after his death, by three civil wars under the four so-called Righty Guided Caliphs (Bakr, Umar, Uthman and Ali), the last three assassinated by unhappy believers, heralding a violent tradition of settling leadership issues, benefitting a religion where violence and the threat of violence is pervasive.
Narrated Said bin Al-Musaiyab:
When the first civil strife (in Islam) took place because of the murder of 'Uthman, it left none of the Badr warriors alive (the first real battle for control of the Peninsula).
When the second civil strife, that is the battle of Al-Harra, took place, it left none of the Hudaibiya treaty companions alive.
Then the third civil strife took place and it did not subside till it had exhausted all the strength of the people.
Both types of wars, the general war against unbelievers and the bloody, pitiless conflicts between believers which continue in one form or another to this day, with the second type expected to continue indefinitely, even if Islam is successful in ridding the world of all of those who refuse to submit to the Will of Allah.
A saying of Muhammad meant to ease the conscience of those, who, in their zeal to rid the world of Allah's enemies, slaughter the innocent, in ever increasing numbers, even those who have submitted to the Will of Allah hoping to save themselves:
Allah's Apostle said, "An army will invade the Ka'ba and when the invaders reach Al-Baida', all the ground will sink and swallow the whole army."
I said, "O Allah's Apostle! How will they sink into the ground while amongst them will be their markets (the people who worked in business and not invaders) and the people not belonging to them?"
The Prophet replied, "all of those people will sink but they will be resurrected and judged according to their intentions."