The Zaporizhian Cossacks became particularly strong in the first quarter of the 17th century under the leadership of hetman Petro Konashevych-Sahaidachny, who launched successful campaigns against the Tatars and Turks. Tsar Boris Godunov had incurred the hatred of Ukrainian Cossacks by ordering the Don Cossacks to drive away from the Don all the Ukrainian Cossacks fleeing the failed uprisings of the 1590s. This contributed to the Ukrainian Cossacks' willingness to fight against him. In 1604, 2000 Zaporizhian Cossacks fought on the side of the Polish-Lithuanian Commonwealth, and their proposal for the Tsar (Dmitri I), against the Muscovite army. By September 1604, Dmitri I had gathered a force of 2500 men, of whom 1400 were Cossacks. Two thirds of these "cossacks", however, were in fact Ukrainian civilians, only 500 being professional Ukrainian Cossacks. On July 4, 1610, 4000 Ukrainian Cossacks fought in the Battle of Klushino, on the side of the Polish-Lithuanian Commonwealth. They helped to defeat a combined Muscovite-Swedish army and facilitate the occupation of Moscow from 1610 to 1611, riding into Moscow with Stanisław Żółkiewski.