Before the nineteenth century, most European political borders reflected dynastic inheritance, marriage alliances and territorial conquest, with a single state routinely containing several genuinely different linguistic and cultural groups, and a single cultural nation routinely split across several different states' borders. Nineteenth-century nationalism spread a genuinely new political principle: that each culturally or linguistically defined nation deserved its own sovereign state, ideally matching political borders to cultural and linguistic ones rather than to dynastic inheritance, and that principle helped drive the unification of previously fragmented territories into single nation-states within a matter of decades.
Nationalism reframed political legitimacy around shared culture rather than dynastic right
Where earlier political legitimacy had rested substantially on a ruling dynasty's inherited right to govern whatever territory it happened to control, nationalist thought instead grounded political legitimacy in a shared national identity, common language, culture, history and a sense of collective belonging, arguing that a people sharing that identity had a genuine right to self-governance within their own unified state. This was a genuinely new basis for political legitimacy, one that made a fragmented patchwork of small, culturally related states or a large multi-ethnic empire look like a problem to be actively corrected rather than simply an inherited arrangement to be accepted.
This principle actively drove real, rapid political unification and fragmentation alike
Nationalist movements drove the political unification of previously fragmented, culturally related territories into single, unified nation-states within a genuinely short span of decades, while the same underlying principle simultaneously put real pressure on large, multi-ethnic empires containing several distinct national groups, since nationalism's logic implied those groups deserved their own separate states rather than remaining under one shared imperial government. This dual effect, driving unification in some places and fragmentation pressure in others, is exactly why nineteenth-century nationalism reshaped Europe's political map so extensively within such a genuinely compressed historical timeframe.
What we're still unsure about
That nationalism reframed political legitimacy around shared national identity, and that this principle drove real unification and fragmentation pressures across nineteenth-century Europe, are well established, extensively documented findings in political and diplomatic history. What's more genuinely a matter of ongoing historical debate is exactly how much nationalist sentiment itself actively drove these political changes versus how much political and economic elites strategically invoked nationalist rhetoric to justify unification projects they were already pursuing for other, more material reasons, and historians continue to actively debate that relative weighting for specific nineteenth-century unification movements rather than the causal balance being fully settled.
This sits inside Nationalism & the Formation of Nation-States, one of eight topics in Modern History, one of seven domains in History, one of seventeen subjects the app can quiz you on.