Six years ago, the Russian navy formed a new army corps whose job it would be to defend Kaliningrad, Russia’s geographically separate outpost on the Baltic Sea between Poland and Lithuania. This year, when the war in Ukraine began to go badly for Russia, the Kremlin yanked the 11th Army Corps from Kaliningrad and sent it into Ukraine. Where the Ukrainian army quickly destroyed it. The formation, deployment and destruction of the 11th Army Corps tell a story that’s bigger than the tragic tale of Russia’s war in Ukraine. The corps, sandwiched between two NATO countries along a strategic sea,...