To propagate political or religious theories, to crush them out, or to
defend them;

To increase the influence and power of the state by acquisitions of
territory;

To defend the threatened independence of the state;

To avenge insulted honor; or,

From a mania for conquest.

It may be remarked that these different kinds of war influence in some
degree the nature and extent of the efforts and operations necessary for
the proposed end. The party who has provoked the war may be reduced to
the defensive, and the party assailed may assume the offensive; and
there may be other circumstances which will affect the nature and
conduct of a war, as,--

1. A state may simply make war against another state.

2. A state may make war against several states in alliance with each
other.

3. A state in alliance with another may make war upon a single enemy.

4. A state may be either the principal party or an auxiliary.

5. In the latter case a state may join in the struggle at its beginning
or after it has commenced.