Nationalism is not only a modern concept, but also a natural and eternal part of the human psyche. It has absolutely no roots in human biology. For hundreds of thousands of years, Homo Sapiens and its ancestors lived in small intimate communities comprising no more than a few dozen people.
Studies show that human beings tend to develop loyalty to small intimate groups such as tribes or a family business than to millions of citizens. To cultivate and preserve mass loyalty, therefore, a nation must do a great deal of social (re)construction.