For four centuries, the Polish-Lithuanian state encompassed a major geographic region comparable to present-day Poland, Lithuania, Belarus, Ukraine, Russia, Latvia, Estonia, and Romania. Governed by a constitutional monarchy that offered the numerous nobility extensive civil and political rights, it enjoyed unusual domestic tranquility, for its military strength kept most enemies at bay until the mid-seventeenth century and the country generally avoided civil wars. Selling grain and timber to western Europe helped make it exceptionally wealthy for much of the period.

The...