If only a province, or a military position, or an army, be attacked, it is simply regarded as taking the _initiative_ in offensive movements.
_Offensive_ war is ordinarily most advantageous in its moral and political influence.

It is waged on a foreign soil, and therefore spares the country of the attacking force; it augments its own resources at the same time that it diminishes those of the enemy; it adds to the moral courage of its own army, while it disheartens its opponents.

A war of invasion may, however, have also its disadvantages.

Its lines of operation may become too _deep_, which is always hazardous in an enemy's country.

All the natural and artificial obstacles, such as mountains, rivers, defiles, fortifications, &c., are favorable for defence, but difficult to be overcome by the invader.