In March 1968, Bongo declared Gabon a one-party state by dissolving the BDG and establishing a new party—the Gabonese Democratic Party. He invited all Gabonese, regardless of previous political affiliation, to participate. Bongo was elected president in February 1975 and re-elected in December 1979 and November 1986 to seven-year terms. In April 1975, the office of vice president was abolished and replaced by the office of prime minister, who has no right to automatic succession. Under the 1991 constitution, in the event of the president's death, the prime minister, the National Assembly president, and the defense minister share power until a new election is held. Using the PDG as a tool to submerge the regional and tribal rivalries that have divided Gabonese politics in the past, Bongo sought to forge a single national movement in support of the government's development policies.