The quirk that All Might possesses is called All For One. It is a quirk that can be passed from one person to another and it gains more power each time it is passed. All Might gave Deku (Izuku) a sliver of his power by making him eat one of his hairs. If this is how it can be passed than isn't possible for that quirk to be passed to a multitude of people? Say, an army, for example.