What was the military strategy involving hired soldiers called during ancient and medieval periods?

During ancient and medieval periods, the military strategy involving hired soldiers is referred to as mercenary warfare. This practice involved recruiting individuals who were willing to fight for financial compensation rather than loyalty to a particular nation, emperor, or cause. Mercenaries could be deployed by various states or city-states to supplement their own armies, allowing for increased military strength without the need for extensive training or the loyalty of drafted citizens.

This strategy often provided advantages in terms of flexibility and immediate military presence, as these hired soldiers could be contracted as needed for specific campaigns. The use of mercenaries was particularly common in regions with frequent conflicts, where the availability of local recruits might be limited. In contrast, conscription involves mandatory service where citizens are required to join the military, a professional army refers to a standing, trained military force compensated through regular salaries, and volunteer forces consist of individuals who choose to enlist out of personal conviction or altruism rather than financial incentive.