According to the "lore" of LoL, cough cough . At least what we used to have,
The Institute of War was established for the sole purpose of arranging political disputes between factions because they realised human's use of magic in warfares is indeed too powerful and detrimental, as demonstrated by the previous Rune War which physically and permanently scarred the land in a few unfix-able fashion so they decided to find a way to keep fightings in-door where they can manage and contain.
By promising different rewards of political gains, redemption, satisfaction and some other things, they successfully persuaded and gathered the most fearsome and enthusiastic group of well known fighters, mystical monsters, demi-gods, the unknowns and some random but strong individuals across the realm all in one place and put them all under the eyes/chain of summoners so they can function properly as pawns for politics without putting the strain on the planet.
Hence the name League of Legends.
But hey, Riot doesn't like that even though it sounds just fine.
