Since independence from Portugal in 1974, Guinea-Bissau has experienced considerable political and military upheaval. In 1980, a military coup established authoritarian General Joao Bernardo 'Nino' VIEIRA as president. Despite eventually setting a path to a market economy and multiparty system, VIEIRA's regime was characterized by the suppression of political opposition and the purging of political rivals. Several coup attempts through the 1980s and early 1990s failed to unseat him. In 1994 VIEIRA was elected president in the country's first free, multiparty election. A military mutiny and resulting civil war in 1998 eventually led to VIEIRA's ouster in May 1999. In February 2000, a transitional government turned over power to opposition leader Kumba YALA after he was elected president in transparent polling. In September 2003, after only three years in office, YALA was overthrown in a bloodlessmilitary coup, and businessman Henrique ROSA was sworn in as interim president. In 2005, former President VIEIRA was reelected, pledging to pursue economic development and national reconciliation; he was assassinated in March 2009. Malam Bacai SANHA was elected in an emergency election held in June 2009, but he passed away in January 2012 from a long-term illness. A military coup in April 2012 prevented Guinea-Bissau's second-round presidential election - to determine SANHA's successor - from taking place. Following mediation by the Economic Community of Western African States, a civilian transitional government assumed power in 2012 and remained until Jose Mario VAZ won a free and fair election in 2014. A long-running dispute between factions in the ruling PAIGC party has brought the government to a political impasse; there have been five prime ministers since August 2015.