Manpower

Manpower is a civ resource representing working-age population available for use. Each production building, like a logging camp, requires 1 manpower for operation, and "building" a new unit consumes 1 manpower (while disbanding a unit refunds 1 manpower).

If a unit is damaged through combat or morale loss (desertion), it may require some additional manpower to be restored to full quality. Typically this will be a fraction of the original cost: e.g. it may need 0.4 manpower.

A small amount of manpower is produced in villages each week based a civ's fertility rate, which can be augmented by certain buildings, resources, and, technologies.

Gameplay Rationale
A civ which is frequently at war must grapple with finding a way to resupply its armies, which cannot simply regenerate their health after spending a few turns without moving. This is both more realistic and more interesting, and it means that even a militarily weaker combatant with superior manpower can potentially prove victorious in a war of attrition.