The Teutonic Knights were a natural ally of Švitrigaila as they wanted to undo the Polish–Lithuanian union, established in 1385, which led to their defeat in the 1410 Battle of Grunwald and 1422 Gollub War. Švitrigaila began talks with the Knights soon after the death of Vytautas and kept sending envoys to Prussia. However, Grand Master Paul von Rusdorf delayed and consulted with the Livonian Order, Sigismund, Holy Roman Emperor, prince-electors, and Pope Martin V. Livonian Order advised to support Švitrigaila but also not to sever the relationship with Poland, Sigismund and prince-electors supported the alliance, while the pope opposed it. Towards the end of May 1431, Rusdorf personally met with Švitrigaila but again refused to enter into an agreement motivating that he needed to discuss the proposals with Prussian estates. Rusdorf's reluctance could be explained by Poland's attempts to form a Polish–Teutonic alliance against Švitrigaila. Eventually, the treaty was concluded on 19 June 1431 in Christmemel. The treaty established a military alliance: if one party was attacked, the other was obliged to defend; war is declared only if both parties agree; any peace agreement would apply to both parties equally; spoils of war would be divided equally. The treaty had no expiration and would survive the deaths of Švitrigaila and Rusdorf if their heirs confirmed the agreement. The treaty was signed by Rusdorf, Livonian Master Zisse von Rutenberg, and Prussian bishops. On the Lithuanian side it was signed by Švitrigaila, his brother Lengvenis and cousin Sigismund Kęstutaitis, Lithuanian bishops and nobles. Nine Lithuanian nobles were: castellan of Vilnius Kristinas Astikas, elder of Vilnius Jurgis Gedgaudas, elder of Samogitia Mykolas Kęsgaila, voivode of Trakai Jaunius Kęsgaila, castellan of Trakai Sungaila, land marshal Rumbaudas Valimantaitis, Chodko Jurewicz, regent of Navahrudak Petras Mangirdaitis, court marshal Jonas Goštautas.
Aftermath
Following the Treaty of Christmemel, the Knights invaded Poland and ravaged the Dobrzyń Land before suffering a defeat in the Battle of Nakel in September 1431. At the same time Polish army invaded Volhynia and besieged Švitrigaila in the Lubart's Castle in Lutsk. Švitrigaila proposed peace and a formal two-year Truce of Staryi Chortoryisk was signed on 1 September. The treaty of 1431 was confirmed again in Christmemel on 15 May 1432. The second treaty had 50 witnesses, however historians noted that some prominent figures of Lithuanian nobility, including Kristinas Astikas, were missing. This is interpreted as a sign of growing opposition to Švitrigaila's reign. Indeed, a group of nobles organized a coup and deposed of Švitrigaila in August 1432. The Knights formally observed the Truce of Staryi Chortoryisk, but also continued to support Švitrigaila, mostly through the Livonian Order. Their alliance was decisively defeated in the Battle of Pabaiskas in September 1435.