Between 1953 and 1956, the North Vietnamese government instituted various agrarian reforms, including "rent reduction" and "land reform", which resulted in significant political repression. During the land reform, testimony from North Vietnamese witnesses suggested a ratio of one execution for every 160 village residents, which extrapolated across all of Vietnam would indicate nearly 100,000 executions. Because the campaign was concentrated mainly in the Red River Delta area, a lower estimate of 50,000 executions became widely accepted by scholars at the time, but declassified documents from the Vietnamese and Hungarian archives indicate that the number of executions was much lower, although likely greater than 13,500. In the South, Diệm countered North Vietnamese subversion (including the assassination of over 450 South Vietnamese officials in 1956) by detaining tens of thousands of suspected communists in "political reeducation centres". This program incarcerated many non-communists, but was successful at curtailing communist activity in the country, if only for a time. The North Vietnamese government claimed that 2,148 people were killed in the process by November 1957. The pro-Hanoi Việt Cộng began a guerrilla campaign in South Vietnam in the late 1950s to overthrow Diệm's government. From 1960, the Soviet Union and North Vietnam signed treaties providing for further Soviet military support.