In February 1440 the nobility of Warmia and the town of Braunsberg (Braniewo) co-founded the
Prussian Confederation, which opposed Teutonic rule, and most towns of the Prince-Bishopric joined the organization in May 1440. In February 1454, the organization asked Polish King
Casimir IV Jagiellon to incorporate the region to the Kingdom of Poland, to which the king agreed and signed the act of incorporation in
Kraków on 6 March 1454, and the
Thirteen Years' War (1454–1466) broke out. During the war Warmia was recaptured by the Teutonic Knights, however, in 1464 Bishop
Paul of Lengendorf sided with Poland and the Prince-Bishopric came again under the overlordship of the Polish King. In the
Second Peace of Thorn (1466) the Teutonic Knights renounced any claims to the Prince-Bishopric, and recognized Polish sovereignty over Warmia, which was confirmed to be part of Poland. So the third of its diocesan territory forming the prince-episcopal
temporalities was disentangled from Teutonic Prussia, while the other two thirds of the diocese proper remained within the Order State, which according to the peace treaty also became part of the Kingdom of Poland as a
fief and protectorate. The prince-bishopric became part of the newly established Polish province of
Royal Prussia, and later also became part of the larger
Greater Poland Province of the Polish Crown. The bishops insisted on keeping their imperial privileges and ruled the territory as
de facto prince-bishops although the Polish king did not share this point of view. This led to conflict when the Polish king claimed the right to name the bishops, as he did in the
Kingdom of Poland. The chapter did not accept this and elected
Nicolaus von Tüngen as bishop, which led to the
War of the Priests (1467–1479) between King
Casimir IV Jagiellon (1447–1492) and Nikolaus von Tüngen (1467–89) who was supported by the
Teutonic Order and King
Matthias Corvinus of Hungary. The Polish king accepted Tüngen as prince-bishop in the
First Treaty of Piotrków Trybunalski, while Tüngen inversely accepted the Polish king as sovereign and obliged the chapter to elect only candidates approved by the Polish king. However, when Tüngen died in 1489, the chapter elected
Lucas Watzenrode as bishop and
Pope Innocent VIII supported Watzenrode against the wishes of
Casimir IV Jagiellon, who preferred his son
Frederick. This problem finally led to the Exempt Status of the bishopric in 1512 by
Pope Julius II. In the
Second Treaty of Piotrków Trybunalski (7 December 1512) Warmia conceded to King
Alexander Jagiellon a limited right to propose four candidates to the chapter for the election, who however had to be native Prussians. Renowned Polish astronomer
Nicolaus Copernicus lived in the prince-bishopric, in the towns of
Lidzbark,
Olsztyn and
Frombork, and there he began and completed his groundbreaking work on
heliocentrism. In 1521 Copernicus commanded the successful Polish defense of Olsztyn during a
siege by the Teutonic Knights during the
Polish–Teutonic War (1519–1521). The Diocese of Warmia lost the two thirds of its diocese within Teutonic Prussia after 1525 when the Order's Grand Master
Albert of Brandenburg-Ansbach converted the monastic state into
Ducal Prussia, himself ruling as duke. On 10 December 1525, at their session in Königsberg, the
Prussian estates established the
Lutheran Church in Ducal Prussia by deciding the
Church Order. Thus Bishop
Georg von Polenz of Pomesania and Samland, who had converted to Lutheranism in 1523, took over and introduced the
Protestant Reformation also in the ducal two thirds of Warmia diocese, territorially surrounding the actual prince-episcopal third. With the formal abolition of the now Lutheran bishopric of Samland in 1587 the now Lutheran Warmian parishes became subject to the Sambian
Consistory (later moved to Königsberg). The Congregation of St. Catherine, founded at Braniewo by
Regina Protmann, engaged in education, especially schooling for girls. In this period the
cathedral chapter mostly elected bishops of Polish nationality. The faithful in the northern part of the diocese were by large majority ethnic
Germans, while in the remainder they were overwhelmingly
Poles. Following King
Sigismund III's contract on regency in Ducal Prussia (1605) with
Joachim Frederick of Brandenburg, and his
Treaty of Warsaw (1611) with
John Sigismund of Brandenburg, confirming the co-enfeoffment of the Berlin Hohenzollern with Ducal Prussia, these two rulers guaranteed free practice of Catholic religion in all of prevailingly Lutheran Ducal Prussia. Some churches were reconsecrated to or newly built for Catholic worship (e.g.,
St. Nicholas, Elbląg,
Propsteikirche, Königsberg). Those new Catholic churches located in the ducal two thirds of Warmia diocese and in diocesan territory of the suppressed Samland see were then subordinated to the Warmian Frombork see. This development was recognised by the Holy See in 1617 by de jure extending Warmia's jurisdiction over Samland's former diocesan territory, only containing few immigrated Catholics. In practice the ducal government obstructed Catholic exercise in many ways. Five Prince-Bishops of Warmia resigned from their position to become
Archbishops of Gniezno and
Primates of Poland, the highest representatives of the Catholic Church in Poland. , leading poet of
Polish Enlightenment and last Prince-Bishop of Warmia As a result of the
First Partition of Poland in 1772, Warmia was annexed by the
Kingdom of Prussia, and in 1773 incorporated into its newly formed province of
East Prussia as
bishopric of Ermland. ==Aftermath==