 It took Sigismunt II's unilateral declaration of the incorporation into the Polish Crown of substantial disputed border regions, including most of Lithuanian Ukraine, to make the Lithuanian magnates rejoin the process, and participate in the swearing of the act of the Union of Lublin on July 1, 1569.Lithuania for the near future was becoming more secure on the eastern front.It's increasingly Polonized nobility made in the coming centuries great contributions to the Commonwealth's culture, but at the cost of Lithuanian national development.