Kyiv and Warsaw are united in the face of Russia’s aggression against Ukraine, yet they have still not resolved the historical disputes that divide them. Their shared border cuts across former imperial lands whose multicultural fabric was undermined by the rise of nation states, each aiming for a kind of ethnic uniformity within their respective territories.

The memory of the violence that ensued remains vivid today. During the successive partitions of the Polish-Lithuanian Commonwealth (also called the Republic of Two Nations) towards the end of the 18th century, the Russian autocracy and the Habsburg monarchy largely carved up this area. Poles and Ukrainians continued to live side by side in Austrian Galicia and in Volhynia, within the Russian empire. The influence of the old Polish elites remained strong, however, especially in urban centres, which had big Jewish populations, while Ukrainians were mainly concentrated in the countryside.

This diversity did not fit easily into nationalist projects based on ethnic homogeneity, whether it was the Poles’ dream of restoring their lost state, or the desire of Ukrainians to create one of their own. As a result, the creation of the two states in their present form occurred in the 1940s through ethnic cleansing – part of the huge cycle of violence and population displacements across Europe that began with the first world war in 1914 and ended only in the late 1940s.

Rivalries between Ukraine and Poland emerged as empires collapsed after the first world war. In November 1918 soldiers of the Polish Legions fought Ukrainian nationalists at the Battle of Lviv (in Ukrainian) or Lwów (in Polish). The nascent Polish Republic and the West Ukrainian People’s Republic both claimed sovereignty over Eastern Galicia and the Carpathians, formerly under Austro-Hungarian rule.

At Versailles, the Allied powers recognised Poland’s independence and discussed how its eastern border should be defined. The (…)

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