When the first Crusaders entered Syria in 1097 AD, the first scholars to raise their voices and warn of the potentially disastrous consequences of the Crusade, were in Damascus. Among them was Ali Ibn Tahir al-Sulami. Al-Sulami wrote one of the earliest treatises (Kitab al Jihad) on the jihad in response to the Crusade.
Al-Sulami, who preached in Damascus until his death, interpreted the Crusade as a divine warning to test the willingness of the Muslims to refrain from committing acts that God forbade and to under take the duty of jihad, which they had neglected. He warned his contemporaries that if they did not act immediately, while the enemy was still weak and far from his sources of supply, they would not be able to uproot him.
Al-Sulami, who established the theoretical foundations of the Countercrusade, did not live long enough to see the results of his teachings. However, he sowed the seeds of national and religious renaissance, which passed from one generation of scholars to another.