On February 24, 2022, Russia launched the largest land invasion in Europe since 1945. To anyone who had not been paying attention to the previous fifteen years, the move was a shock. To anyone who had been reading the geographic literature, the surprise was not that it happened but how exactly it unfolded.

Russia's strategic problem — the same one its rulers have wrestled with since the Grand Duchy of Moscow in the 14th century — is that the North European Plain runs uninterrupted from Poland to the Urals, with no mountain range, no major river, and no narrow defensive corridor between Russia's heartland and any well-armed western neighbor that decides to march east. Napoleon used that plain in 1812. The German Army used it in 1914 and again in 1941.

Russia's traditional answer has been to push its frontier as far west as it can manage, ideally to a defensible feature: the Carpathian Mountains, the Vistula River, the Baltic coast.