The PDRE was established in February 1987 as a Marxist-Leninist one-party state upon the adoption of the 1987 Constitution, three weeks after approval in the national referendum. The Derg, the military junta that had ruled Ethiopia as a provisional government since 1974, planned for transition into a civil government and proclaimed a socialist republic in 1984 after five years of preparation. The Workers' Party of Ethiopia (WPE) was founded that same year as a vanguard party led by Derg chairman Mengistu Haile Mariam. The Derg was dissolved but continued to rule "de facto" until September when the new government took office, three months after the June general election. It was dominated by surviving Derg members, with Mengistu as both President of Ethiopia and General Secretary of the WPE.