Traditionally, Moldavia had been a subject of the Kingdom of Poland, and later the Polish–Lithuanian Commonwealth. As the Ottoman influence grew in the 16th century, they had become more and more interested in the region. From the end of the 16th century and the beginning of the 17th century, the
magnates of the Polish–Lithuanian Commonwealth
intervened in the affairs of Moldavia, which the Ottoman Empire considered within its
sphere of influence. Additionally, the Ottomans were aggravated by the constant raids of
Cossacks, then nominally subjects of the Commonwealth, across the border into Ottoman territories. Another reason causing the war was the recent outbreak of the Thirty Years' War, and the request of support from the Protestant rebel leaders in Bohemia. At the time, the
Thirty Years' War was raging across Europe.
Gabriel Bethlen, prince of
Transylvania saw an opportunity to unite the two Hungarian principalities, Transylvania and
Royal Hungary, and unsuccessfully attacked Vienna in November 1619. He also asked Sultan
Osman II for aid, but this was unsuccessful. The Commonwealth was relatively uninvolved in this war but the Polish king,
Zygmunt III Waza, sent an elite and ruthless mercenary unit, the
Lisowczycy, to aid his
Habsburg allies. They defeated the Hungarian lord
George Rákóczi at the
Battle of Humenné in 1619, and thus, cut the supply lines of Transylvanian forces. Then
Gaspar Graziani, ruler of
Moldavia, switched sides and joined Poland. Thus, the sultan agreed to help Bethlen, gathering a large Ottoman army with the intent of a punitive invasion of the Commonwealth. ==War==