 Additionally, the Ottomans were aggravated by the constant raids by Cossacks, then nominally subjects of the Commonwealth, across the border into Ottoman territories.In the meantime, the Thirty Years' War raged across Europe.The Commonwealth was relatively uninvolved in this war but the Polish King Sigismund III Vasa sent an elite and ruthless mercenary unit, the "Lisowczycy", to aid his Habsburg allies in Vienna, since his brother-in-law was the Emperor.