justs it to the
exigencies of the occasion. Sometimes, however, diplomacy fails, either
because the conflicting policies are really irreconcilable, or because
passion, prejudice, national ambition, or international misunderstanding
induces the citizens of both States and their rulers so to regard them.
In that case, if neither State is prepared so to deflect its policy as
to avert collision, war ensues. The policy remains unchanged, but the
means of further pursuing it, otherwise than by an appeal to force, are
exhausted. War is thus, according to the famous definition of
Clausewitz, the pursuit of national policy by other means than those
which mere diplomacy has at its command--in other words by the conflict
of armed force. Each State now seeks to bend its enemy's will to its own
and to impose its policy upon him.

The means of pursuing this policy vary almost indefinitely. But inasmuch
as war is essentially the conflict of armed force, the primary object of
each belligerent must in all cases be to subdue, and, in the last
resort, to destroy the armed forces of the adversary. When that is done
all is done that war can do. How to do this most speedily and most
effectively is the fundamental problem of war. There is no cut-and-dried
solution of the problem, because although war may be considered, as it
has been considered above, in the abstract, it is the most concrete of
all human arts and, subject to the fundamental principle above
enunciated, its particular forms may, and indeed must, vary with the
circumstances and conditions of each particular war. Many commentators
on war distinguishing, with Clausewitz, between "limited" and
"unlimited" war, would further insist that the forms of war must vary
with its objects. I cannot follow this distinction, which seems to me to
be inconsistent with the fundamental proposition of Clausewitz, to the
effect that war is the pursuit of policy by means of the conflict of
armed force. If you desire your policy to prevail you must take the best
means that are open to you to make it prevail. It is worse than useless
to dissipate your energies in the pursuit of any purpose, however
important in itself, which does not directly conduce, and conduce better
than any other purpose you could pursue, to that paramount end. The only
limitation of your efforts that you can tolerate is that they should
involve the least expenditure of energy that may be necessary to make
your policy prevail. But