Archaeological findings throughout the area indicate that Senegal was inhabited in prehistoric times. Since then, Senegal has had a varied cultural history of kingdoms, brotherhoods and colonial struggles (between and against colonising powers). Eastern Senegal was once part of the Empire of Ghana. It was founded by the Tukulor in the middle valley of the Senegal River. Islam, the dominant religion in Senegal, first came to the region in the 11th century. In the 13th and 14th centuries, the area came under the influence of the Mandingo empires to the east; the Jolof Empire of Senegal also was founded during this time. Various European powers - Portugal, the Netherlands, and England - competed for trade in the area from the 15th century onward, until in 1677, France ended up in possession of what had become an important slave trade departure point - the infamous island of Gorée next to modern Dakar. Millions of West African tribes people were shipped from here. It was only in the 1850s that the French began to expand their foothold onto the Senegalese mainland, at the expense of native kingdoms such as Waalo, Cayor, Baol, and Jolof. In January 1959, Senegal and the French Sudan merged to form the Mali Federation, which became fully independent on June 20, 1960, as a result of the independence and the transfer of power agreement signed with France on April 4, 1960. Due to internal political difficulties, the Federation broke up on August 20. Senegal and Sudan (renamed the Republic of Mali) proclaimed independence. Léopold Senghor was elected Senegal's first president in September 1960. After the breakup of the Mali Federation, President Senghor and Prime Minister Mamadou Dia governed together under a parliamentary system. In December 1962, their political rivalry led to an attempted coup by Prime Minister Dia. Although this was put down without bloodshed, Dia was arrested and imprisoned, and Senegal adopted a new constitution that consolidated the president's power. In 1980, President Senghor decided to retire from politics, and he handed power over in 1981 to his handpicked successor, Abdou Diouf. Senegal joined with The Gambia to form the nominal confederation of Senegambia on February 1, 1982. However, the union was dissolved in 1989. Despite peace talks, a southern separatist group in the Casamance region has clashed sporadically with government forces since 1982. Senegal has a long history of participating in international peacekeeping.