The reason why North and South American societies are considered to be the most diverse in the world today is because of their History. North America, especially the United States, is an immigrant country, it received thousands of immigrants from very diverse backgrounds in the XIX century: German, Chinese, Italian, Irish, Eastern European, etc. While South America is a mixture of different races: the Spanish conquistadors had children with the native peoples like the Aztecs or the Incas, plus the black slaves that were brought from Africa.