The third and final phase forbade possession of land above for one family. This phase was carried out in April 1948, two months after the Communists took power by force. Farms started to be collectivized, mostly under the threat of sanctions. The most obstinate farmers were persecuted and imprisoned. The most common form of collectivization was "agricultural cooperative" (in Czech "Jednotné zemědělské družstvo", JZD; in Slovak "Jednotné roľnícke družstvo", JRD). The collectivization was implemented in three stages (1949–1952, 1953–1956, 1956–1969) and officially ended with the 1960 implementation of the constitution establishing the Czechoslovak Socialist Republic, which made private ownership illegal.