Finally in 1596 through the Union of Brest a part of the Orthodox Church in Ukraine acknowledged the supremacy of the Pope. There was however great resistance to the new measure, the Orthodox hierarchy was reestablished by the efforts of the faithful and they regarded the Uniat Church as an agent of Polonization. The Academy of Kiev under a series of able leaders, as the Metropolitan Peter Mohyla, did splendid work in maintaining the Faith. Mohyla worked out a form of Orthodox scholasticism which retained most of the Orthodox manner of thinking and was yet available as a weapon again the Polish and Jesuit propagandists. Yet the Academy like the schools of the brotherhoods was never able to break with a narrow ecclesiastical tradition and to launch itself on a program of progressive education. A more effective, if cruder, method of opposition lay in the rise of the Kozaks, peasants who fled to the east to live their lives in freedom as they desired. These men were prepared to fight against any foe, whether he were Pole, Muscovite, Tatar or Turk. At first they were a wild and turbulent group but their leaders finally forged them into an efficient force. Now and then the Kings endeavored to secure their assistance by payments and by enrolling some of them in units in the Polish army but the Kozaks remained independent and a pillar of strength to all Orthodox movements. Finally in the seventeenth century the hetman Bohdan Khmelnitsky won with them for a short time practically complete independence and again Ukraine could breathe freely. Bohdan died before he had established the new state on a firm basis and won for it international recognition. In his last years he found it necessary after the Kozak Wars which started Poland very definitely on the downward path to put himself and the Kozaks more or less under the protection of the Tsar of Russia. There was thus reestablished an official seal on that relationship which had been interrupted when the Tatars invaded Rus four centuries before. The result was none too satisfactory for the autocratic Moscow of the day constantly interfered with the liberties of the Kozaks and in 1667 in a treaty between the Tsar and the King of Poland, Ukraine was again divided between Russia and Poland, with the Dnieper as the dividing line.