At the time of the Reformation the (Turkish) Ottoman Empire reached its greatest heights. After smashing what little remained of the 1000-year Byzantine Empire in the mid-15th century, the Turks made huge inroads into southeastern Europe until they were finally checked at the gates of Vienna in 1529 (as much by the weather as the defenders). These Islamic advances caused great concern in Europe. Luther thus wrote, more than once, about them, and his reflections point us in the right direction.

Since the Turk [Muslim] is the rod of the wrath of the Lord our God and the servant of the raging devil, the first thing to be done is to smite the devil, his lord, and take the rod out of God’s hand, so that the Turk may be found only, in his own strength, all by himself, without the devil’s help and without God’s hand. This should be done by the pious, holy, precious body of Christians. They are the people who have the arms for this war and they know how to use them. If the Turk’s god, the devil, is not beaten first, there is reason to fear that the Turk will not be so easy to beat.

Now the devil is a spirit who cannot be beaten with armor, muskets, horses, and men, and God’s wrath cannot be allayed by them, as it is written in Psalm 33, “His delight is not in the strength of the horse, nor his pleasure in the legs of a man; but the Lord takes pleasure in those who fear him, in those who hope in his steadfast love.” Christian weapons and power must do it. Here you ask, “Who are the Christians and where does one find them?” Answer: There are not many of them, but they are everywhere, though they are spread thin and live far apart, under good and bad princes. Christendom must continue to the end, so it must be possible to find them. Every pastor and preacher ought diligently to exhort his people to repentance and to prayer. They ought to drive men to repentance by showing our great and numberless sins and our ingratitude, by which we have earned God’s wrath and disfavor, so that he justly gives us into the hands of the devil and the Turk. And so that this preaching may work the more strongly, they ought to cite examples and sayings from the Scriptures, such as the Flood, Sodom and Gomorrah, and the children of Israel, and show how cruelly and how often God punished the world and its lands and peoples. And they ought to make it plain that it is no wonder, since we sin more grievously than they did, if we are punished worse than they.

This fight must be begun with repentance, and we must reform our lives, or we shall fight in vain… [F]or God is devising evil [punishment] against us because of our wickedness and is certainly preparing the Turk against us, as he says in Psalm 7, “If a man does not repent, God will whet his sword; he has bent and strung his bow; he has prepared his deadly weapons.” … After people have thus been taught and exhorted to confess their sin and amend their ways they should then be most diligently exhorted to prayer and shown that such prayer pleases God, that he has commanded it and promised to hear it, and that no one ought to think lightly of his own praying or have doubts about it, but with firm faith be sure that it will be heard. -from “On War Against the Turk”