ENAdopted on October 29, 1791 by the Four Years Sejm the Mutual Pledge of the Two Nations formally specified the provisions of the Constitution of May 3. In fact, it was restoring the dualistic state union of the Crown and Lithuania. Despite the catastrophe of 1792, the Mutual Pledge was kept by both nations in the political, military, and spiritual spheres. After about 90 years, Lithuanians began to question the spirit of the Mutual Pledge by launching the processes that led to its termination. These were dramatic processes, as they went against the tradition of the common state and the common struggle for the state’s rebirth. Although they took place in an evolutionary way, there were assigned to them certain turning points, breaking new psychological barriers. The result of these processes was the annihilation of the strata that define themselves as Poles and Lithuanians, and the lack of a group of Polish-speaking Lithuanians. Keywords: Mutual Pledge of the Two Nations, conspiracies and uprisings, manifestations of unity in 1861, the Lithuanian national movement, Polish-speaking Lithuanians. [From the publication]