A French army operating against Spain would have the Pyrenees for its
first base; the line of the Ebro for a second, resting its wings on the
gulf of Gascony and the Mediterranean. If from this position it advance
its left, possessing itself of the kingdom of Valencia, the line of the
Sierra d'Estellas becomes its third base of operations against the
centre of Spain.

A base may be parallel, oblique, or perpendicular to our line of
operations, or to the enemy's line of defence. Some prefer one plan and
some another; the best authorities, however, think the oblique or
perpendicular more advantageous than the parallel; but we are not often
at liberty to choose between these, for other considerations usually
determine the selection.

In 1806, the French forces first moved perpendicular to their base on
the Main, but afterwards effected a change of front, and moved on a line
oblique or nearly parallel to this base. They had pursued the same plan
of operations in the Seven Years' War. The Russians, in 1812, based
perpendicularly on the Oka and the Kalouga, and extended their flank
march on Wiozma and Krasnoi; in 1813, the allies, based perpendicularly
on Bohemia, succeeded in paralyzing Napoleon's army on the Elbe.

An American army moving by Lake Champlain, would be based perpendicular
on the great line of communication between Boston and Buffalo; if moving
from the New England states on Quebec and Montreal, the line of
operations would be oblique; and if moving from the Niagara frontier by
Lake Ontario and the St. Lawrence, the line would be nearly parallel
both to our base and to the enemy's line of defence--an operation, under
the circumstances, exceedingly objectionable.