Why did forage limit the movements of premechanized armies?

Forage was a critical constraint on the movement of premechanized armies because it was the bulkiest supply item required for the animals that provided the military's primary means of transport.1

The limitations imposed by forage were twofold:

• The Multiplier Effect: Because supply trains relied on animal-drawn transport, the animals themselves required significant amounts of food and forage. When an army operated at a distance from its bases, the forage needed to sustain the shuttling supply train would eventually consume all available transport capacity, leaving nothing for the fighting force. This logistical reality effectively limited the operating radius of armies—such as those in the American Civil War—to approximately 100 miles from a base.1
• Dependence on Local Resources: To overcome these transport limits, armies often relied on "living off the country." However, this forced armies to move slowly to avoid exhausting local supplies, and they remained vulnerable in regions where forage was scarce, such as deserts, mountains, or winter landscapes. If an army moved too slowly or was pinned down, it risked starving its own animals and men.2