When Russia attacked Ukraine a few weeks ago, international observers cited all sorts of reasons for the invasion: Vladimir Putin was mad for power; he was concerned that Ukraine would join NATO; he had simply lost his mind. Few paid attention to one of his own chief justifications for why Russia needed to go on the offensive, and against Ukraine specifically.
Even the most aggressive dictators do not start wars without cloaking their tanks in some righteous cause. They do often cite national security, for example the expansion of a rival’s sphere of influence (i.e., NATO). Economic factors often play a role, but these are never a standalone casus belli: it would be hard to motivate men to die for oil. There is always some higher cause. Sometimes this is ideological, like spreading democracy, communism, or Islam. More often, particularly in modern European history, the aggressor is motivated by nationalism.
Starting a war over language may sound strange. But the call to defend or liberate “our people” is a stirring one; indeed, it is the one that has motivated almost every European war in the past 150 years. Who “our people” are can be a thorny topic. Alongside language, people speak of “ethnicity” or “culture.” But in a complicated world with blond Poles and swarthy Germans, what was the best proxy for Adolf Hitler and his ilk to determine who belonged to which ethnicity? And what is the key denominator of a culture, and thus a people? Some racial nationalists may not have liked to admit it, but in the real world, the answer to these questions is virtually always language.
In 1871, the leaders of all the German states proclaimed Wilhelm I their one Kaiser.
Nationalism took Europe by storm in 1848, when Germans, Italians, Hungarians, and many other peoples launched revolutions to win unity and independence. Jacob Grimm, the father of linguistics, played a critical role in 19th Century geopolitics by instilling a common sense of linguistic, and thus national, identity in Germans.
For all of history, Germany had been a patchwork of independent states. The dominant one, Prussia, was determined to change that; their rivals in France were determined to stop them. Chancellor Otto von Bismarck settled the matter with blood and iron. Prussia won a decisive victory in the Franco-Prussian War, which convinced all the German states to swear fealty to Wilhelm I as Kaiser of Germany.
For the next half-century, peace settled over Western Europe. But the Balkans exploded as nations like Serbia, Bulgaria, and Romania threw off Ottoman rule, then fought a series of bloody wars against the Turks and one another to determine who was who. These conflicts were particularly complicated among closely-related South Slavic peoples: millions of people are still bitterly divided over whether Macedonian is a separate language, or a dialect of Bulgarian. The question has geopolitical implications.