Earlier in his reforming career, Luther was actually not an advocate of a war with the Turks. He viewed Turkish advances into Europe as a form of divine punishment for the sins of the church, a view reminiscent of what we find in Christian writings on Islam in the eighth century: "To fight against the Turks is to oppose the judgment God visits upon our iniquities through them." Luther was particularly opposed to a crusade against the Turks under papal oversight. But things changed in the course of the 1520s as the Ottomans made greater inroads into Europe. By the time of the siege of Vienna in 1529, Luther had changed his mind, supporting a war against the Turks, what he referred to as the Türkenkrieg, as long as it was led by princes and not by the church.

Green, Todd H, The Fear of Islam_ An Intro…, loc. 149