Dynastic struggle In 1427, the
Polish nobility initiated an anti-
Jagiellonian opposition and attempted to have
Władysław II Jagiełło's sons
Władysław III and Casimir IV Jagiellon declared illegitimate to the Polish throne as they, being sons of a
Lithuanian noblewoman Sophia of Halshany, had no blood link to the previous ruling Polish dynasty, the
Piasts, however Casimir's father ensured the succession for his sons. Moreover, the death of Casimir's elder brother, Władysław III, at the
Battle of Varna (1444) during a crusade against the
Ottoman Empire, created a potentially dangerous leadership vacuum. Władysław's death left Poland without a clear successor and Casimir was fraught with political manoeuvring and rivalries within the Polish nobility class. After a three-year
interregnum marred by political contestation and negotiations, Casimir was elected King of Poland in 1447. His ascension was supported by key factions, but not without opposition. The
Prussian Confederation, composed of the cities in the region of
Prussia, as well as some nobles, viewed his reign as a shift towards centralisation. Casimir's acceptance of the Polish crown was contingent upon his willingness to adopt a dual role as both King of Poland and Grand Duke of Lithuania, thereby maintaining the balance of power between the two realms. At his coronation on 25 June 1447, Casimir became both the King of Poland and Grand Duke of Lithuania, a position he would hold until his death.
Royal authority The question of the political relationship between Poland and Lithuania was an ongoing handicap throughout Casimir IV's reign. While the two states had been bound together in personal union since the
Union of Krewo (1385), they were politically distinct entities, each with its own laws and institutions. Poland then was more of a
homogenous and Catholic society, whereas Lithuania remained multicultural and a predominantly
Eastern Orthodox dominion that expanded across vast regions once part of the
Kievan Rus. It was also highly decentralised. Casimir worked to harmonise the interests of the Polish and Lithuanian nobility while also maintaining his position as the supreme ruler of both states. The
Tęczyński family often mediated between the crown and the upper class. Their influence ensured that Casimir had strong support within the domestic sphere while advancing his diplomatic agenda abroad. In Lithuania, the Grand Chancellor of Lithuania,
Mikołaj II Radziwiłł, was instrumental in strengthening ties with the Polish Crown while safeguarding Lithuanian autonomy. He was nicknamed "Amor Poloniae" by contemporaries due to his pro-Polish stance and sentiment. Casimir's reign was marked by efforts to enhance cooperation, and he also strived to secure the southern and eastern frontiers, which were constantly threatened by the
Crimean Tatars and the
Grand Duchy of Moscow.
Thirteen Years' War In 1454, Casimir was approached by the Prussian Confederation for aid against the
Teutonic Order, which he promised, by making the separatist
Prussian regions a protectorate of the
Polish Kingdom. However, when the insurgent cities rebelled against the Order, it resisted and the
Thirteen Years' War (1454–1466) ensued. Beginning in 1457, the Teutonic army from
Königsberg unsuccessfully besieged their former seat at
Marienburg and lost the nearby town of Marienburg (Malbork) in effect. At the
Battle of Świecino (
Schlacht bei Schwetzin) in September 1462, the Polish army and hired mercenaries decimated the Teutonic force, simultaneously cutting their future supply routes from
Western Europe. A year later, the Teutonic rescue fleet was sunk at the
Battle of Vistula Lagoon, resulting in the decisive end of the Teutonic Order's navy. In the
Second Peace of Thorn (1466), the declining Order recognised Polish sovereignty over the seceded western Prussian regions,
Royal Prussia, and the Polish crown's overlordship over the remaining
Teutonic Monastic State. It was transformed following Casimir's death into a duchy, which became known as
Ducal Prussia (1525).
Foreign relations and diplomacy Casimir sought to maintain influential relations with the
Habsburgs and the
Holy Roman Empire. In 1454, he married
Elizabeth of Austria, daughter of King
Albert II of Germany and
Elizabeth of Luxembourg, a descendant of King
Casimir III of Poland. Her distant relative was
Frederick III, Holy Roman Emperor. The marriage strengthened the ties between the house of Jagiellon and the sovereigns of Hungary-Bohemia and put Casimir at odds with the emperor through internal Habsburg rivalry. Elisabeth's only brother
Ladislaus, king of Bohemia and Hungary died in 1457, and after that, Casimir and Elizabeth's dynastic interests were directed also towards her brother's kingdoms. The threat from the
Ottoman Empire, which was expanding rapidly in the
Balkans and along the
Black Sea, loomed over
Eastern Europe during Casimir's reign. While Poland-Lithuania did not engage directly in military conflict with the
Turks, Casimir faced increasing pressure from the Ottomans' allies, including the Crimean Tatars, whose raids intensified. He was, nonetheless, able to maintain a semblance of stability on the eastern border, skillfully negotiating with the Muscovites and the
Crimean Khanate to avoid full-scale war. His diplomacy helped prevent the dissolution of the Polish-Lithuanian alliance and ensured territorial integrity. In around 1480, Casimir was allied with the
Great Horde against Muscovy and Crimea; however, his failure to support
Khan Akhmed at the
Great stand on the Ugra River contributed to Russia gaining its independence from the steppe nomads. The intervention of the
Roman curia, which hitherto had been hostile to Casimir, was due to the permutations of
European politics. The pope was anxious to get rid of the
Hussite King of Bohemia, George Podebrad, as the first step towards the formation of a league against the Ottoman Turks. Casimir was to be a leading factor in this combination, and he took advantage of it to procure the election of his son
Vladislaus II as the
King of Bohemia. But he would not commit himself too far, and his ulterior plans were frustrated by the rivalry of
Matthias Corvinus, King of Hungary, who even went so far as to stimulate the
Teutonic Order to rise against Casimir. The death of Matthias in 1490 was a great relief to Poland, and Casimir employed the two remaining years of his reign in consolidating his position still further. In 1490, Casimir's son
John Albert was elected the
King of Hungary by a party among the
Hungarian nobles. He was, however, defeated by his older brother, King Vladislaus II of Bohemia. Casimir, who wanted to secure a separate realm for his sons, proposed John Albert. Most Hungarian barons and prelates preferred Vladislaus because his rule in Bohemia had indicated that he would respect their liberties. Vladislaus was crowned King of Hungary on 18 September 1490 in
Székesfehérvár. == Personal life and appearance ==