Konrad, the Polish duke of Mazovia, hopes to strengthen Polish Latin-rite Christianity and Poland’s position in regard to its neighbors.

Konrad is the youngest son of High Duke Casimir II the Just of Poland and Helen of Znojmo, daughter of the Přemyslid duke Konrad II of Znojmo (ruler of the Znojmo Appanage in southern Moravia, part of Duchy of Bohemia).

His maternal grandmother was Maria of Serbia, apparently a daughter of the pre-Nemanjić župan Uroš I of Rascia.

After his father's death in 1194, Konrad had been brought up by his mother, who had acted as regent of Masovia.

He had received Masovia in 1199 and in 1205 also the adjacent lands of Kuyavia.

In that year, he and his brother, Duke Leszek I the White of Sandomierz, had had their greatest military victory at the Battle of Zawichost against Prince Roman the Great of Galicia–Volhynia.

The Ruthenian army had been crushed and Roman had been killed in battle.

The Rurik princess Agafia of Rus became his wife.

In order to enlarge his dominions, Konrad had unsuccessfully attempted to conquer the adjacent pagan lands of Chelmno in Prussia during a 1209 crusade with the consent of Pope Innocent III.

The monk Christian of Oliva had in 1215 been appointed a missionary bishop among the Old Prussians; his residence at Chelmno had been devastated by Prussian forces the next year.

Several further campaigns in 1219 and 1222 had failed, involving Konrad in a long-term border quarrel with the Prussian tribes.

The duke's ongoing attempts on Prussia have been answered by incursions across the borders of his Masovian lands, while Prussians are in the process of gaining back control over the disputed Chelmno Land and even threaten Konrad's residence at Plock Castle.

Subjected to constant Prussian raids and counter-raids, Konrad now wants to stabilize the north of his Duchy of Masovia in this fight over the border area of Chełmno.

Thus in 1226, Konrad, having difficulty with constant raids over his territory, invites the religious military order of the Teutonic Knights to fight the Prussians, as they already had supported the Kingdom of Hungary against the Cuman people in the Transylavanian Burzenland from 1211 to 1225.

When the Knights notified Hungary that the Order was firstly responsible to the pope, they had been expelled by the Hungarian king Andrew II.

Thus, in return for the Order's service, Grand Master Hermann von Salza wants to have its rights documented beforehand, by a deal with Konrad that is to be confirmed by the Holy Roman Emperor and the Roman Curia.

Duke Konrad of Mazovia, failing to grasp the danger of the Knights’ presence, had at first supported the Knights against Pomerania, but eventually shifts his alliance.

…Mazovia with Cuiavia, …

Mazovia, together with its county of Plock, remains an independent Piast duchy until 1329, when it comes under Bohemian rule.

Poland’s King Casimir III succeeds in reincorporating into the royal fief Bohemian-controlled Mazovia, …

Poland loses the recently acquired duchy of Mazovia, …

The old part of Warsaw (Stare Miasto), on the west bank of the Vistula, occupied since the tenth century and first documented in the twelfth century when it was the residence of the dukes of Mazovia, is built around the market square (Rynek) and is enclosed by walls erected in 1380.

Wladyslaw II Jagiello, Grand Duke of Lithuania and King of Poland, has joined two states that have become the leading power of eastern Europe.

In Poland, the nobility has strengthened its position, especially during the latter part of Wladyslaw's reign, and Wladyslaw has been unable to win the burghers to his side and use them politically as a counterweight to the nobles.

In questions of national religion the king has showed resoluteness, particularly in his attempt to suppress the Polish followers of Jan Hus.

Continually, he has played his hand cautiously: although he had supported the Hussites during the decade of the 1420s in their struggle against King Sigismund of Bohemia and Hungary, for example, he had refrained from intervention.

Wladyslaw, who dies on May 31/June 1, 1434, ends his reign with good relations between Poland and Hungary.

His eldest son, ten years old, succeeds him as Wladyslaw III.

A Polish faction opposes the installment of Albert Habsburg as Holy Roman Emperor and king of Bohemia and Hungary, their choice being Wladyslaw III of Poland.

Wladyslaw is only fourteen; most of the major decisions are either made or manipulated by the regent, Zbigniew Olesnicki, who is a powerful Polish noble, bishop of Kraków, and had also been a close adviser to his father.

The forces of Wladyslaw and Albert prepare for war, but the brewing Polish-Bohemian conflict ends with Albert’s death from dysentery in 1439 while fighting the Turks in Hungary.

Albert has left his wife pregnant, and a crisis immediately develops concerning his succession to the throne of Hungary.

The Hungarian nobles choose Wladyslaw, who is supported by the successful aristocratic general Janos Hunyadi, whom Albert had recently appointed military governor (ban) of Severin in Wallachia.