in 1768, the polish–lithuanian commonwealth became a protectorate of the russian empire. control of poland was central to catherine the great's diplomatic and military strategies. attempts at reform, such as the four-year sejm's may constitution, came too late. the country was partitioned in three stages by the neighboring russian empire, the kingdom of prussia, and the habsburg monarchy. by 1795, the polish–lithuanian commonwealth had been completely erased from the map of europe. poland and lithuania were not re-established as independent countries until 1918.