Within the borders of Tanzania co-exist approximately 120 ethnic groups speaking languages representing all four major African language groups. These include Khoisan, or “click”speaking hunter-gatherers, Nilotic-speaking pastoralists (such as the Maasai), Cushitic speakers, and Bantu speakers; the latter predominate in terms of population size. The largest ethnic groups include the Sukuma (over three million), and the Chagga, Haya, and Nyamwezi (over one million each). Despite the tremendous cultural and linguistic diversity among Tanzanians, ethnic groups are united by the use of a common language—Swahili—and a sense of national identity. The growing number of refugees (from neighboring Rwanda, Burundi, and Uganda in particular) do not appear to have caused serious ethnic tensions, but they have become a serious strain on the economy and the local environment.