In July 1968, he arrested Captain Ngouabi, dissolved the National Assembly and the Political Bureau of the MNR and suspended the 1963 Constitution. This resulted in a confrontation between supporters of the Civil Defense and part of the army. He was then forced to amnesty all political prisoners and deal with his opponents. Following the coup tensions remained between Massamba-Débat's administration and the military and on September 4, 1968 Massamba-Débat's government was overthrown by Marien Ngouabi, the chairman of the same party that had brought Massamba-Débat to power.