Peru is a multiethnic country formed by the combination of different groups over five centuries, so people in Peru usually treat their nationality as a citizenship rather than an ethnicity. Amerindians inhabited Peruvian territory for several millennia before Spanish Conquest in the 16th century; according to historian David N. Cook their population decreased from an estimated 5–9 million in the 1520s to around 600,000 in 1620 mainly because of infectious diseases. Spaniards and Africans arrived in large numbers under colonial rule, mixing widely with each other and with indigenous peoples. With about 29.5 million inhabitants, Peru is the fourth most populous country in South America. Its demographic growth rate declined from 2.6% to 1.6% between 1950 and 2000; population is expected to reach approximately 42 million in 2050. As of 2007, 75.9% lived in urban areas and 24.1% in rural areas. Major cities include Lima, home to over 8 million people, Arequipa, Trujillo, Chiclayo, Piura, Iquitos, Cusco, Chimbote, and Huancayo, all of which reported more than 250,000 inhabitants in the 2007 census. The largest Peruvian communities are in the United States (Peruvian Americans), South America (Argentina, Chile, Venezuela and Brazil), Europe (Spain, Italy, United Kingdom and France), Japan, Australia and Canada.