independently of the others, and seeks distinct and separate objects,
each must have its own independent theatre of operations.

A war between France and Austria may embrace all Italy and Germany, but
the theatre of operations may be limited to only a portion of these
countries. Should the Oregon question lead to hostilities between the
United States and England, the theatre of war would embrace the greater
part of North America and the two oceans, but the theatre of operations
would probably be limited to Canada and our northern frontier, with
naval descents upon our maritime cities.

The first point to be attended to in a plan of military operation is to
select a good _base_. Many circumstances influence this selection, such
as mountains, rivers, roads, forests, cities, fortifications, military
dépôts, means of subsistence, &c. If the frontier of a state contain
strong natural or artificial barriers, it may serve not only as a good
base for offensive operations, but also as an excellent line of defence
against invasion. A single frontier line may, however, be penetrated by
the enemy, and in that case a second or third base further in the
interior becomes indispensable for a good defence.

A French army carrying on military operations against Germany would make
the Rhine its first base; but if driven from this it would form a second
base on the Meuse or Moselle, a third on the Seine, and a fourth on the
Loire; or, when driven from the first base, it would take others
perpendicular to the front of defence, either to the right, on Béfort
and Besançon, or to the left, on Mézières and Sedan. If acting
offensively against Prussia and Russia, the Rhine and the Main would
form the first base the Elbe and the Oder the second, the Vistula the
third, the Nieman the fourth, and the Dwina and the Dnieper the fifth.