The influence of rivers, forests, swamps, and steppes on the conduct
of military operations is as old as war itself. Ever since wars have
been waged, every commander, of high and low echelons alike, has logically utilized natural terrain features to his own advantage and the enemy's disadvantage. The defender, as the weaker party, entrenched him~el:f behind natural lines of resistance which would hamper the enemy's approach and conduct of operations as much as possible. By
preference, the defender anchored his exposed flanks on the formidable natural obstacles presented by watercourses or forests. The attacker, on the other hand, sought out terrain favorable for approach marches find combat. He avoided large forest and swamp areas; he outflanked the enemy who sat behind natural or artificial obstacles; he, so to
speak, maneuvered the enemy out of position.
A study of military history reveals that prior to World War I very
few river crossings were forced in the face of the enemy. The explanation is easy enough. Before World War I armies were relatively small. In most instances, there was no reason for forcing a
crossing against any enemy who had chosen a watercourse as his natural line of resistance. The watercourse could be crossed much more
l'apidly and with less trouble at a place which the enemy had chosen
not to hold at all, or at best with only a handful of troops. A similar
situation prevailed in the case of large forest and swamp areas. As
long as armies were relatively small, exceptional circumstances had
to arise before the commander decided.
