Most Americans take it for granted that there is an American people or nation with its own particular culture and traditions, and that the human race in the world as a whole is divided among culturally distinct peoples or nations.
The twenty-first century is the era of the nation-state. Today there are 193 members of the United Nations General Assembly, even though at the time of its formation, the UN had only fifty-one members. Where did those 142 members come from, in the last seventy-seven years? The new states were formed from the partition of former European empires like the British and French Empires, the disintegration of the Soviet Union, which was the successor state to the Romanov Russian Empire, and in some cases, like those of Yugoslavia and Sudan, the disintegration of post-colonial successor states into even smaller states.
Many of the post-colonial successor states have inherited the borders of former empires, sometimes drawn deliberately by European colonial administrators to split some ethnic nations and throw others together, as part of divide-and-rule schemes. As a result, many post-colonial countries in Africa and the Middle East—like Pakistan, Afghanistan, Iraq, Syria, Nigeria, and others—lack any ethnonational majority and have often been held together by dictatorships of one kind or another. In some cases, entire ethnic nations like the Kurds and Roma find themselves with no nation-state of their own, scattered as tolerated or abused national minorities among a number of countries.
In spite of all of this, most post-imperial successor states are less ethnically diverse than the former empires as a whole, and many fit a broad definition of a nation-state, in which a majority, though not necessarily all, of the citizens belong to a common linguistic and cultural community whose members may but do not necessarily share a common ancestry.