Kosiński uprising (1591–1593) was the first Cossack rebellion in the Polish–Lithuanian Commonwealth, commanded by the Cossack Hetman Krzysztof Kosiński.
Prelude
In the late 16th century, the Polish–Lithuanian Commonwealth was experiencing a short period of internal stability. This, however, was threatened by the Cossacks, who organised raids into Crimea, Moldavia, and other lands of the Ottoman Empire. To counter the threat, Sultan Murad III threatened Poland–Lithuania with war if the Cossack pillaging continued.
In 1580 the Sejm in Warsaw passed the Order in Ukraine (Porządek ze strony Niżowców i Ukrainy) Act, in which Registered Cossacks were banned from raids to the Zaporizhian Sich, taking captives or pillaging. Any Cossack who broke this law was to be put to death without trial.
The uprising
The immediate cause of the uprising was a dispute between the Cossack hetman Krzysztof Kosiński and the starosta of Bila Tserkva and Voivode of Volyn, Janusz Ostrogski. Kosinski, a nobleman from Podlasie, received lands in the Rokitno area, abandoned after the Crimean Tartar invasions, from Hetman Jan Zamoyski in 1590. However, these lands were taken over by Aleksander Wiśniowiecki and later ceded to Janusz Ostrogski. King Sigismund III Vasa appointed a commission to put down the rebellion, headed by Mikołaj Jazłowiecki. In 1592, after unsuccessful negotiations, Kosinski continued fighting, destroying Ostrogski's estates. The final battle took place on 2 February 1593 at Piatek, where Kosinski's army was defeated by Janusz Ostrogski. After the surrender, The self-proclaimed hetman did not keep the terms of capitulation and fled to Zaporizhia , where he gathered a 2,000-strong detachment of Cossacks. He established contacts with Russia and Tatars , seeking support against the Commonwealth everywhere .But in May 1593 he was finally defeated at Cherkasy by Alexander Wisniowiecki and died in unclear circumstances.