the study of his profession. He was no mere professor, but a soldier bred
in the severest school of war. The pupil and friend of Sharnhorst and
Gneisenau, he had served on the Staff of Blücher in 1813, he had been Chief
of the Staff to Wallmoden in his campaign against Davoust on the Lower
Elbe, and also to the Third Prussian Army Corps in the campaign of 1815.
Thereafter for more than ten years he was Director of the General Academy
of War at Berlin, and died in 1831 as Chief of the Staff to Marshal
Gneisenau. For the fifty years that followed his death his theories and
system were, as he expected they would be, attacked from all sides. Yet
to-day his work is more firmly established than ever as the necessary basis
of all strategical thought, and above all in the "blood and iron" school of
Germany.

The process by which he reached his famous theory can be followed in his
classical work _On War_ and the _Notes_ regarding it which he left behind
him. In accordance with the philosophic fashion of his time he began by
trying to formulate an abstract idea of war. The definition he started with
was that "War is an act of violence to compel our opponent to do our will."
But that act of violence was not merely "the shock of armies," as
Montecuccoli had defined it a century and a half before. If the abstract
idea of war be followed to its logical conclusion, the act of violence must
be performed with the whole of the means at our disposal and with the
utmost exertion of our will. Consequently we get the conception of two
armed nations flinging themselves one upon the other, and continuing the
struggle with the utmost strength and energy they can command till one or
other is no longer capable of resistance. This Clausewitz called "Absolute
War." But his practical experience and ripe study of history told him at
once that "Real War" was something radically different. It was true, as he
said, that Napoleon's methods had approximated to the absolute and had
given some colour to the use of the absolute idea as a working theory. "But