The history of Southern Africa has been divided into its prehistory, its ancient history, the major polities flourishing, the colonial period, and the post-colonial period, in which the current nations were formed. Southern Africa is bordered by Central Africa, East Africa, the Atlantic Ocean, the Indian Ocean, and the Sahara Desert. Colonial boundaries are reflected in the modern boundaries between contemporary Southern African states, cutting across ethnic and cultural lines, often dividing single ethnic groups between two or more states.