Why are the Champions doing battle?

Okay, so I am pretty new to this game and am loving it. main, and am having a ton of fun. But recently, I was just supporting my adc and thought: "Hm.. Why are these champions fighting? Why are these entities, heroes and monsters doing battle against one another?" There was some stuff about old lore and that being revoked and the situation is kind of hazy. I would still keep playing this game no matter whether I know why they're fighting or not; some of you may argue that you don't really need a purpose ( I agree to a certain extent ), but when I play a game, I like to dive heavy into its lore and the backstory and I find it makes it a heap more fun and a more rich experience. So, in conclusion: Does anyone know why the Champions are fighting? I know that like, say, likes war and destruction so that is why he likes fighting but as a whole, why do the champions do battle? If anyone knows the answer and could tell me, I think that would greatly enrich my experience with League as a whole. Thanks.