The Republic of Liberia fronts on to the Atlantic Ocean for some 560 km to the southwest and is bordered to the northwest by Sierra Leone, to the north by Guinea, and to the east by Côte d'Ivoire. Portuguese explorers visited Liberia's coast in 1461 and, during the next 300 years, European merchants and Africans engaged in trade. Today sixteen ethnic groups make up 95% of the Liberian population. Americo-Liberians (descendants of former U.S. slaves) make up approximately 2.5% of the population, and Congo People (descendants of former Caribbean slaves) 2.5%. Traditional religions are practiced by about 70% of the population, 30% of whom also follow Christian religions, 10% are Christian and 20% Muslim. English is the official language, but African languages are used extensively. The history of modern Liberia dates from 1816, when the American Colonization Society, a private United States organization, was given a charter by the United States to send freed slaves to the west coast of Africa. The first wave of emancipated slaves who landed in Liberia was western influenced and educated, alien in origin, life-style, culture, language, religion and habits to the indigenous Africans. In many respects, they re-created an American society in Liberia and Monrovia, the capital, was named after President Monroe. The original settlers who survived in the first wave of immigration formed the nucleus of the settler population and the ruling minority until 1980.