Mercenaries are hired soldiers who usually take no affiliation with any organization or government. They fight by their contracts, which they need to fulfill in order to earn money. Mercenaries are often hired by wealthy landlords, band leaders and individuals alike, with purposes ranging from personal security to manhunts and as an attempt to display power.
From the Ancient Ages, mercenaries were employed by empires, who wanted to assemble their armies from multiple nations. In times when conquests and oppression was abundant, instability in regular armies would quickly lead to rebels and the collapse of the main defense. People who operated independently from any nation, army and culture and were solely interested making their combat skills worthwhile, were easy to recruit and use to any military purpose by anyone. Not needing to provide the most necessary equipments and the need of only paying hard cash, the convenience of mercenaries were favoured among many political figures.In Medieval Ages, the vast numbers of empires and country inequalities between them was a deciding factor when it came to fighting wars. Numerous areas, which were important trade hubs in the continent, had to rely on their wealth when defending themselves, as they were either too small or lacked a war industry. A great example of this is the Netherlands, which used Swiss pikeman mercenaries to defend from outside threats.
There were also specialized units for mercenary purposes, such as Albanian stradiots, Finnish hackapells and German Black Riders. They were independently acting groups, serving as a unit to their recruiters until dissolved or merged into regular armies several centuries later.