The French revolution and the Napoleonic wars ushered in the age of nationalism and transformed the capabilities and roles of states. Clausewitz spent a lifetime pondering these changes and their implications for warfare. Almost alone among his contemporaries, Clausewitz understood the destructive nature of modern warfare and the difficulty of limiting and stopping wars once popular passions became engaged. The challenge to nineteenth-century statesmen was to find some way to allow the major European powers to reorganize themselves into a community of nation states without provoking a catastrophic, continental war. On War, Clausewitz's principal work, was intended, in part, to alert contemporaries to this danger, but its author remained deeply pessimistic about its reception and of the ability of leaders to grasp and respond appropriately to the changed nature of warfare.

Clausewitz is considered the preeminent theorist of war, and generations of military officers and strategists have studied his magnum opus. On War and the History of the Peloponnesian War are the only works written before the twentieth century that are standard fare on reading lists of staff and war colleges around the world.