The League of Legends was created at the end of the last Rune War, as a way to prevent another involving destructive rune magic that threatened to destroy Runeterra. It does not completely outlaw all war, but merely steps in to limit and "referee," so to say, how far wars can go. It is mostly concerned with use of destructive rune and leyline magic, and places severe sanctions on nations that decide to use these potentially world threatening magics.
The League also settle disputes between the Valoranian nations. Nations send Champions to battle on the Fields of Justice in such disputes, where they can fight each other without actually causing death. These disputes vary in size, ranging from a single match to month long conflicts involving hundreds of matches. The League often declares peace edicts over regions involved in disputes, to ensure war doesn't erupt and the outcome of the dispute is honored.
The Institute of War[]
The League is housed in the Institute of War. It is located in the center of Valoran, between the nations of Demacia and Noxus. This location gives it geographic and political power and positioning, allowing it to more easily oversee the affairs of Valoran.
The Fields of Justice[]
The matches of the League are held on the Fields of Justice. These fields include the Summoner's Rift, the Howling Abyss, the Crystal Scar, and the Twisted Treeline. They are maintained by the League and hold magic that allow the Champions to attack each other without causing permanent physical damage.
Summoners[]
Summoners are trained in the Institute and assist Champions they mentally link to with strategic advice and magic. They are powerful mages who are highly sought after by the differing factions of Valoran to represent them in League disputes, as well as for their advice in political matters and magical prowess. The Institute of War has become the largest center of magical learning and research. It is in the Institute where the summoners are trained and research magic. It holds many secrets of magic and artifacts within, granting it much prestige and power.