Bolesław IV of Warsaw

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Bolesław IV Warszawski (Bolesław IV of Warsaw) (1421 - September 10, 1454) was a Polish duke of Masovia. He inherited territories of his grandfather, Janusz I of Warsaw.

Son of Bolesław Januszowic and Anna Holszańska, married to Barbara, father of Konrad III Rudy, Kazimierz III Płocki, Janusz II Płocki, Bolesław V Warszawski and Anna, wife of Przemysław II Cieszyński.

At first he tried to stay neutral in conflicts between the Teutonic Order and Kingdom of Poland (allied with Grand Duchy of Lithuania), but soon he was forced to chose sides and sided with Poland. For a time his aggressive policies (desire to take over the Podlasie region) threatened a war between Masovia and Lithuania, but the mediation of Polish diplomats. For a time he was a candidate in the free election to the Polish throne, opposing Casimir IV Jagiellon (Grand Duke of Lithuania), but eventually Bolesław decided to withdraw and supported Casimir, in order to ensure the defeat of another contender, Frederick II, Elector of Brandenburg.