An excellent article in the New York Times magazine:
No law can exist for a millennium without being broken, and there are scattered historical reports, mostly from Christian chroniclers, of Muslim forces acting outside the bounds of lawful jihad, without the authorization of the scholars. Men were always considered legitimate targets, and Muslim armies sometimes slaughtered them just as Muslims could be slaughtered by their enemies. Remarkably enough, though, the legal principles of jihad protecting women, children and fellow Muslims survived well into the modern era, when the secular regimes of the Muslim world began to fight according to secular ideas. The World War I Armenian genocide, which took place in the last, secularizing gasp of the declining Ottoman Empire, was the first really substantial systematic violation of the ban on killing women and children in recorded Islamic history.
This is yet another example of one of the great ironies of secularism. Secularists, particularly militantly atheist ones, constantly posit religion as a source of violence and evil, and yet the historical record very clearly shows, even in the case of Islam, that religion tends to be a mitigating factor in reducing the level of violence that is integral to every human conflict between rival forces.
By any means necessary is not a religious notion, it is a fundamentally secular one. For only secularism knows no inherent bounds upon it and it is this secular notion that has released the world’s militaries from past strictures of civilized behavior.