A Jolof Empire ruled parts of Senegal from 1350 to 1549. Various European powers, including Portugal, the Netherlands, France, and Great Britain, competed for trade in the area from the 15th century onward. A slave station on the island of Goree, next to modern Dakar, was used as a base to purchase slaves from the warring chiefdoms on the mainland. Having abolished slavery in 1815, the French began to expand onto the Senegalese mainland in the second half of the 19th century and made it a French colony. The French colonies of Senegal and French Sudan were merged in 1959 and granted independence in 1960 as the Mali Federation. The union broke up after only a few months. Senegal joined with The Gambia to form the nominal confederation of Senegambia in 1982. The envisaged integration of the two countries was never implemented, and the union was dissolved in 1989. The Movement of Democratic Forces in the Casamance has led a low-level separatist insurgency in southern Senegal since the 1980s. Several attempts at reaching a comprehensive peace agreement have failed to resolve the conflict but, despite sporadic incidents of violence, an unofficial cease-fire has remained largely in effect since 2012. Senegal remains one of the most stable democracies in Africa and has a long history of participating in international peacekeeping and regional mediation. Senegal was ruled by the Socialist Party of Senegal, first under President Léopold Sédar SENGHOR, and then President Abdou DIOUF, for 40 years until Abdoulaye WADE was elected president in 2000. He was re-elected in 2007 and during his two terms amended Senegal's constitution over a dozen times to increase executive power and weaken the opposition. His decision to run for a third presidential term sparked a large public backlash that led to his defeat in a March 2012 runoff with Macky SALL. A 2016 constitutional referendum reduced the term to five years with a maximum of two consecutive terms for future presidents - the change did not apply to SALL's first term. SALL won his bid for re-election in February 2019; his term will end in 2024. A month after the election, the National Assembly voted to abolish the office of the prime minister. Opposition organizations and civil society have criticized the decision as a further concentration of power in the executive branch at the expense of the legislative and judicial branches.