Nationalism
The claim that humanity divides naturally into nations and that each nation deserves its own state, an idea barely two centuries old that redrew every map on earth.
Nationalism is the belief that humanity comes divided into nations, that each nation has one rightful political expression, and that the borders of the state should therefore match the borders of the nation. It sounds like a description of the world. It is actually a proposal, and a recent one. In 1750 almost nobody in Europe believed it. Today it is the unstated assumption behind the United Nations, the passport in your pocket, and roughly every war of the last two centuries.
Before it, people were subjects of a ruler, members of a faith, and residents of a village, in that order. A Habsburg peasant owed loyalty to the emperor, not to Austria. Nationalism proposed that the horizontal bond between strangers who share a language and a past outranks the vertical bond to a dynasty. That is a genuinely strange idea, and once believed it is almost impossible to unbelieve.
Where it came from
Three things converged around 1800.
The French Revolution turned the king's subjects into the nation's citizens and then, in the levee en masse of 1793, drafted them. Mass conscription is nationalism's proof of concept: an army of citizens who believe the country is theirs will out-fight a professional army that is paid.
German romantics, above all Johann Gottfried Herder, supplied the theory. Each people, Herder argued, has a Volksgeist expressed in its language and folklore, and a culture flattened into French court manners is a culture killed. This was written as cultural pluralism. It was read, later, as a claim about blood.
And Napoleon exported it by accident. Occupying Germany, Italy, Spain, and Poland, he taught them all the same lesson: a nation in arms wins. The revolt against France was organized in the vocabulary France had supplied.
Two kinds, and why the difference matters
The civic version says the nation is everyone inside the borders who accepts the political contract. France and the United States are the reference cases, and Ernest Renan's 1882 formula captures it: a nation is a daily plebiscite, a matter of choosing to continue together, not of ancestry.
The ethnic version says the nation exists prior to the state, defined by language, descent, and memory, and the state's job is to gather it. Germany and most of Central and Eastern Europe are the reference cases, for the obvious reason that there was no German state to be a citizen of until 1871.
The distinction is real but never clean, and the second version has an ugly implication built in. If the state must match the nation, then people inside the borders who belong to a different nation are a problem to be solved. Population transfer, forced assimilation, and ethnic cleansing are not perversions of ethnic nationalism. They are its engineering solutions.
What it did to the map
It destroyed empires. Multinational states, Habsburg, Ottoman, Romanov, could survive anything except the belief that each of their peoples deserved its own flag. The 1848 revolutions failed but set the agenda. Italy unified by 1871, Germany the same year, and the Balkans spent a century detaching from Istanbul.
Then it went global. Wilson's self-determination was meant for Europe and was immediately picked up by everyone in the colonies who could read, which is how the same principle that broke Austria-Hungary in 1918 broke the British Raj in 1947 and the French empire after that. Nationalism is the most successful political idea in modern history, measured purely by adoption.
The echo
Benedict Anderson's phrase for a nation is an imagined community: too large for its members ever to meet, yet felt as intimate enough to die for. He meant imagined, not fake. Nations are constructed and they are real, in the way money is constructed and real.
That is why announcements of nationalism's death keep failing. Globalization was supposed to dissolve it, and instead the last two decades produced Brexit, Catalan and Scottish independence movements, Hindu nationalism in India, and a Russian war justified by the claim that Ukrainians are not a separate nation. When a state cannot deliver prosperity or order, the one thing it can always offer is belonging. Nationalism is the cheapest legitimacy on the market, and that is exactly why it never goes away.