Nation and state are different things. A state is a territorial monopoly on legitimate coercion; a nation is a community of people who imagine themselves as sharing a culture, language, history, and political fate. The two rarely coincide cleanly: the Habsburg or Ottoman empires were states without a nation, the German-speakers of 1800 were a nation scattered across hundreds of statelets. The nation-state — the assertion that a state's legitimacy derives from its alignment with a single nation — is a nineteenth-century European invention, crystallized by the French Revolution and the unifications of Germany and Italy, that has, in two centuries, become the only form of political organization granted full legitimacy in international law.
Benedict Anderson's Imagined Communities (1983) is the canonical analysis. Nations are 'imagined' because no member ever meets most of the others, yet feels solidarity with them; 'communities' because the imagined relationship is horizontal, comradely, worth dying for — even as real societies remain steeply unequal. Crucially, the nation is also imagined as limited (it has borders, beyond which lie other nations) and sovereign (it answers to no higher dynastic or religious authority), which is why it could only arise once the divine right of kings and the universal church had lost their grip. The technologies that made nations possible were print capitalism (newspapers and novels in vernacular languages, which let strangers picture a simultaneous national 'we' moving through the same 'empty, homogeneous time'), mass schooling (which standardized a single dialect into a national language and instilled patriotic narratives), universal conscription (which mixed regional populations and made them feel national), and the nineteenth-century state's increased reach into ordinary life (postal services, censuses, identity papers, standardized time and currency). The principle ran outward: Woodrow Wilson's 'self-determination' in 1919 dismantled the multinational empires, and the post-1945 wave of decolonization made the nation-state the global default — even where, as in Africa, the 'nation' had to be invented after the state. Yet the United Nations is in fact a United Nation-States; the system has no formal place for nations that lack states (Kurds, Tibetans, Palestinians, Uyghurs) or for states that cover multiple nations (every former colonial state in Africa, the European empires).
The fit between nation and state is always imperfect, and the politics of the twenty-first century is largely the politics of that imperfection. Secessionism (Catalonia, Scotland, Quebec). Nationalist backlash against immigration. Diasporic loyalties mobilized across borders. Transnational identities (European, Muslim, Indigenous). Supranational bodies like the EU pooling sovereignty the nation-state once monopolized. The nation-state remains the default unit, but it is visibly creaking under pressures — migration, climate, capital flows, digital networks — that route straight through borders it was designed to control.