Here's an ironic tidbit from Martin Luther, Hitler's Spiritual Ancestor, by Peter F. Wiener. In this section Wiener is chastising Luther in regard to the Peasants War. Recall, the tumult and slaughter of the peasants increased in 1525. In fact, the section of Wiener's book the following excerpt comes from is entitled, "1525 and all that."
No, Luther would not retract a single word of his pamphlet or apologise for it as the offspring of momentary passion. Instead, he began to elaborate his new political theory, a theory which was so readily accepted in Germany. “Scripture speaking figuratively”, wrote Luther in 1526, “calls rulers drovers, taskmasters, and scourgers. Like the drivers of donkeys, who have to belabour the donkeys incessantly with rods and whips, or they will not obey, so must the ruler do with the people; they must drive, beat, throttle, hang, burn, behead and torture, so as to make themselves feared and to keep the people in check" (E15, 276).
The princes obeyed. A “brutal revenge” took place. Typical is the assertion of one of the princes: “I hope we are now going to play with heads as the boys play with marbles.”
Note the words "new political theory" "wrote Luther in 1526" and then in the next paragraph, "The princes obeyed." Wiener appears to be saying in 1525 the princes obeyed Luther's advise given a year later in 1526 from a sermon Luther gave on the use of the law. The "brutal revenge" sounds suspiciously like the events of 1525. While it's true the Peasants war extended into 1526, it doesn't seem like Wiener means 1526. As to the prince quote "I hope we are now going to play with heads as the boys play with marbles" you can find it here, used in the context of 1525, but without documentation (in a Roman Catholic source). I wouldn't be at all surprised to find out this Roman Catholic source was where Wiener got the quote.
If Wiener meant only Luther's 1525 treatise, "Against The Robbing And Murdering Mobs of Peasants," Luther's harsh advise came out after the wars began. That is, the princes were already in progress of using their force to kill the peasants to suppress their revolt. The book was delayed in printing. For more on this, see this link.