A country is considered developed country when it has a high degree of social, economic development (in some cases sustentable also). During the 21st century, humanity has undergone an evolution in social and economic concepts of the countries, the Cold War was a major contributor to the social division of countries. At the end of the century was the concept of "human development index", which aims to rank countries by their life quality. In the 21st century, a country is classified as developed it reaches a very high HDI (above 0.900).