The year 1303 saw the third Mongol invasion of Syria by Ghazan Khan. What has been called Ibn Taymiyyah's "most famous" "fatwā" was issued against the Mongols in the Mamluk's war. Ibn Taymiyyah declared that jihad against the Mongol attack on the Malmuk sultanate was not only permissible, but obligatory. The reason being that the Mongols could not, in his opinion, be true Muslims despite the fact that they had converted to Sunni Islam because they ruled using what he considered 'man-made laws' (their traditional Yassa code) rather than Islamic law or "Sharia", whilst believing that the Yassa code was better than the Sharia law. Because of this, he reasoned they were living in a state of jahiliyyah, or pre-Islamic pagan ignorance. The fatwa broke new Islamic legal ground because "no jurist had ever before issued a general authorization for the use of lethal force against Muslims in battle", and was to influence modern Islamists in the use of violence against self-proclaimed Muslims.