A medieval war demanded an officially written declaration. Polish war declarations from the time of war with the Teutonic Order are an integral part of war and political culture of that time. In construction the declarations were written analogically to ones in neighbouring countries. They were written in Latin, sometimes in German. In 1454 a gauche Polish language made its presence. In the last war of the Order (1519–1521), the documents were uniformly in Polish and the royal chancellery attempted with some success to establish a uniform model for the drafting of war declarations.
In 1427, the Carthusian monk Heinrich Beringer complained to the Grand Master Paul von Rusdorf that the Teutonic Knights allowed Prussians to continue worshipping the old gods. When asked about this matter, the commanders were to answer: "Let Prussian be Prussians." The existence of relics of old cults is also indicated by synodal and act sources, e.g. the Toruń Peace document from 1411. Recently, Michael Brauer questioned the survival of paganism in Prussia until the 15th century. According to him, the available information was only a creation constructed by the authors of said sources. This is also the opinion of Stephen Rowell and Darius Baronas in relation to Lithuania. They do not notice, however, that it is only early-age modern sources that expand pagan pantheons and associate folk customs with paganism. In Prussia, the language situation was conducive to maintaining relics of paganism – priests did not know Prussian.
Přemysl Otakar II was the first of the Czech Přemyslid kings to turn his attention to Lithuania. Incidentally, Heidenreich Bishop of Chelmno from the Order of the Teutonic Knights stayed at his court; in 1253 he crowned the Lithuanian duke Mindaugas. The king came to the aid of the Teutonic Knights against the Prussians at the turn of 1254/1255 and for the second time in 1267/1268, when the eventual Christianisation of Lithuania also played an important role in his ultimately unsuccessful plans to establish a capital in Olomouc. The knightly King John of Luxembourg marched three times (1329, 1336/1337, 1344/1345) against the Lithuanians together with the Order of the Teutonic Knights and forces from western Europe. Undoubtedly of interest is the letter of Charles IV to Grand Duke Algirdas dated 21 April 1358, when he addressed him as monarcha mundi with an offer of baptism.