Bolesław IV of Warsaw

Bolesław IV of Warsaw (Polish: Bolesław IV warszawski; c. 1421 – 10 September 1454), was a Polish prince member of the House of Piast in the Masovian branch. He was Duke of Warsaw during 1429–1454 (under regency until 1436) and sovereign Duke of Podlachia in 1440–1444.

He was the second son of Bolesław Januszowic (in turn second son of Janusz I of Warsaw) and Anna Feodorovna of Ratnie, a Lithuanian princess (granddaughter of Algirdas).

The successive deaths of his older uncle, father and brother between 1422–1427 left Bolesław IV as the only surviving male heir of Janusz I, who in order to protect his rights, in 1428 forced his local nobility to paid homage to the seven-year old prince as his future ruler; thanks to this, when the Duke died one year later (8 December 1429), Bolesław IV could assumed the power without much difficulties; however, because he was a minor at that moment, his mother Anna took the regency on his behalf until 1436, when he attained his majority and began his personal rule.

In foreign policy, Bolesław IV initially tried to stay neutral in the conflicts between the Teutonic Order and the Kingdom of Poland (and his ally the Grand Duchy of Lithuania), but soon he was forced to choose a side in 1431, at the outbreak of the Polish–Teutonic War. Bolesław IV then decided to send auxiliary troops to the Polish King. The Peace of Brześć Kujawski, signed on 31 December 1435, guaranteed the inviolability of Bolesław IV's domains.

In subsequent years, Bolesław IV was involved in the political intrigues at the Kingdom of Poland, moreover, closely related with the Polish–Lithuanian union. Bolesław IV strongly supported to the party led by the Bishop of Kraków, Zbigniew Oleśnicki. The Duke of Warsaw's adherence to the Bishop of Kraków was noted in his participation in the Confederation of Nowy Korczyn in April 1438. He refused to send troops to the Hussite confederates led by Spytek of Melsztyn at the Battle of Grotniki.

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