In 1569, the new Polish-Lithuanian Commonwealth encompassed virtually the whole of what is today Poland, Belarus, Ukraine, and most of the Baltic states. For the Lithuanian and Polish nobles who constituted this first version of the "nation," it was a capacious notion, tolerating varied language, religious, and political loyalties. Its core character, Snyder contends, endured until the 1863 revolution, surviving even the eighteenth-century partitions that erased the commonwealth from the map. The rise of ethnic nationalism following 1863 undid the earlier openness, culminating in the mass killing of Jews in Vilnius and Jews and Poles in western Ukraine under the Nazis and after. Snyder's ultimate query in this fresh and stimulating look at the path to nationhood is how the bitter experiences along the way, including the bitterest -- ethnic cleansing -- are to be overcome. A wise contemporary Polish leadership has managed by accepting its borders to the east and letting go of the history that produced them, while seeking its future through integration into the West.