Task: Question Generation
Input (English): Passage: In that situation the Teutonic Knights were able to recover the eastern part of Prussia, including the Königsberg towns of Altstadt and Löbenicht on April 17, 1455. They were aided by rebellions in the cities, caused by new large war taxes. The last East Prussian town loyal to the Polish king, Kneiphof, was taken on June 14, 1455 after a long siege by the Teutonic Knights commanded by Heinrich Reuss von Plauen the Elder. The Poles suffered defeat after defeat, and they later also lost Warmia . However, the Grand Master was unable to pay his mercenaries and they took Marienburg, Dirschau, and Eylau  in May 1455. Mercenaries under the Bohemian Ulrich Czerwonka  immediately started negotiations with Poland to discuss selling the castles. The international situation also became significantly worse. On March 25, Emperor Frederick III banned the Prussian Confederation, forbidding trade with its members. On September 24, 1455, Pope Callixtus III warned that he would excommunicate the Prussian Confederation and all its allies unless they made peace with the Order. In June 1455 the Teutonic Knights gained a new ally, King Christian I of Denmark, who declared war against Poland and the Prussian Confederation. This meant nothing more than a disturbance in trade, however, since Denmark was still busy fighting with Sweden.
Output (English): Which event occurred first, Pope Callixtus III warned that he would excommunicate the Prussian Confederation or Teutonic Knights gained a new ally, King Christian I of Denmark?