 The Commonwealth's struggles with the Cossacks were being paid attention to at Moscow's Kremlin, which from the late 1620s began regarding Cossacks as a potent source of fundamental instability in the Polish – Lithuanian rival and neighbor. Russian efforts to destabilize the Polish Kingdom using Cossacks in the 1630s were not yet successful, even though the Cossack elders themselves often raised the possibility of a union with the Tsardom to pressure Poland's ruling elites. The borderlands with Russia had become a place of refuge for Cossacks persecuted after their failed uprisings; regiments of Russian-registered Cossacks, following the Commonwealth example, were eventually established there.
