European exploration of tropical areas was aided by the New World discovery of quinine, the first effective treatment for malaria. Europeans suffered from this disease, but some indigenous populations had developed at least partial resistance to it. In Africa, resistance to malaria has been associated with other genetic changes among sub-Saharan Africans and their descendants, which can cause sickle-cell disease. The resistance of sub-Saharan Africans to malaria in the southern United States and the Caribbean contributed greatly to the specific character of the Africa-sourced slavery in those regions.