Since independence from Portugal in 1974, Guinea-Bissau has experienced considerable political instability. In 1980, a military coup established authoritarian dictator Joao Bernardo 'Nino' Vieira as president. Several coup attempts through the 1980s and early 1990s failed to unseat him, and in 1994 Vieira was elected president in the country's first free elections. But four years later he was ousted after he dismissed his army chief, thereby triggering a civil war that was eventually ended after foreign mediation led to a truce and free elections in January 2000. The next month saw the transitional government turning over power to opposition leader Kumba Yala following two rounds of transparent presidential elections. In September 2003, after only three years in office, Yala was ousted by the military in a bloodless coup, and businessman Henrique Rosa was sworn in as interim president. Former President Vieira was re-elected president in 2005 but was assassinated in March 2009, and he was replaced by Malam Bacai Sanha who won the June 2009 presidential elections and the July runoff. Political instability and mismanagement have undermined the country’s economy that is dependent on primary crops - mainly cashew nuts - and subsistence agriculture. Guinea-Bissau remains one of the world's poorest countries, with more than two-thirds of its population living below the poverty line.