It is understood through archaeology, anthropology, genetics, and linguistics, and since the advent of writing, from primary and secondary sources . Humanity's written history was preceded by its prehistory, beginning with the Palaeolithic Era ("Old Stone Age"), followed by the Neolithic Era ("New Stone Age").
Yet, by the end of the Ice Age, some 12,000 years ago, humans had colonized nearly all ice-free parts of the globe. Beginning around 10,000 BCE, the Neolithic Revolution marked the development of agriculture, which fundamentally changed the human lifestyle.
Francis Fukuyama, in a 1992 best-selling book, proclaimed The End of History, the victory of free-market economics, and the permanent ascendancy of Western liberal democracy. But it soon became evident, writes Allison, that "the end of the Cold War [had] produced a unipolar moment, not a unipolar era.