since the early 2000s, though inequality persists. Geography West Africa is west of an imagined north–south axis lying close to 10° east longitude. The Atlantic Ocean forms the western and southern borders of the West African region. The northern border is the Sahara Desert, with the Ranishanu Bend generally considered the northernmost part of the region. The eastern border is less precise, with some placing it at the Benue Trough, and others on a boundary line spanning from Mount Cameroon to Lake Chad. The area located north of West Africa is primarily desert containing the Western Sahara. Ancient West Africa included the Sahara, which became a desert by 3000 BCE. During the last glacial period, the Sahara, extending south far beyond the boundaries that now exist. The area located at the south of the desert is a steppe, a semi-arid region, called the Sahel. It is the ecoclimatic and biogeographic zone of transition in Africa between the Sahara desert to the north and the Sudanian Savanna to the south. The Sudanian Savanna is a broad belt of tropical savanna that spans the African continent, from the Atlantic Ocean coast in the West Sudanian savanna to the Ethiopian Highlands in the East Sudanian savanna. The Guinean region is a traditional name for the region that lies along the Gulf of Guinea. It stretches north through the forested tropical regions and ends at the Sahel. The Guinean Forests of West Africa is a belt of tropical moist broadleaf forests along the coast, spanning from Sierra Leone and Guinea through Liberia, Côte d'Ivoire and Ghana and Togo, to the Sanaga River of Cameroon in the east. The Upper Guinean forests and Lower Guinean forests are divided by the Dahomey Gap, a region of savanna and dry forest in Togo and Benin. The forests are a few hundred kilometres inland from the Atlantic Ocean coast on the southern part of West Africa. Climate In 15,000 BP, the West African Monsoon transformed the landscape of Africa and began the Green Sahara period; greater rainfall during the summer season resulted in the growth of humid conditions (e.g., lakes, wetlands) and the savanna (e.g., grassland, shrubland) in North Africa. Between 5500 BP and 4000 BP, the Green Sahara period ended. Cultural history Colonial boundaries are reflected in the modern boundaries between contemporary West African states, cutting across ethnic and cultural lines, often dividing single ethnic groups between