Crusades a Barbarian Invasion

The Crusades were nothing more than a 200-year barbarian invasion of the East, territories to which the West had no claim whatsoever. The Crusades were characterised by indiscriminate slaughter, torture, enslavement and looting. In fact, this "holy war" destroyed what was left of the Christian Byzantine Empire. Western civilisation did benefit, however, from the culture, wealth and wisdom of the East. I remember being taught about the Crusades at school: "the good Christians fighting off the evil Muslims". I wonder what is being taught in Muslim schools?