Second, the Crusaders were not extremists or barbarians indulging in thoughtless violence, rather the underlying rationale of the Crusades was relatively sophisticated, elaborated theologically by Christian nations that were threatened by Muslim invaders who had managed to reach into the heart of Europe, in central France in the eighth century. The Crusades were a response to the desecration of the Christian shrines in the Holy Land, the destruction of churches, and the general persecution of Christians in the Near East. A Crusade to be considered legitimate had to fulfill strict criteria; one did not enter into it lightly for self aggrandizement. There had to be a legally sound reason. It was, in other words, waged for purposes of repelling violence or injury and the imposition of justice on wrongdoers. A Crusade was never a war of conversion, rather a rightful attempt to recover Christian territory which had been injuriously seized in the past. Only a recognized authority could formally declare a Crusade, and it had to be waged justly.