In the 15th century, Portuguese people came to Gorée Island off the coast of Dakar. In the 17th century, French people and Dutch people came there, too. These European countries used the island as a trading post in slaves from the mainland, controlled by the Muslim Wolof Empires. Slavery was later made illegal by France, but soon after, around 1850, the French started to conquer the Wolof. By 1902 Senegal was a part of the French colony French West Africa.