> not a single country should interfere with this

I'd rather say "a single country should not interfere with this". IF we have a "simple" internal conflict between local factions, then it should be an international community (the UN, or an agreed conference of major international and local powers) that steps in and ensures mediation. However, this happens very rarely. The reasons it happens very rarely is that major powers such as US, China, Russia, pretty much always have some opposing interests even in local conflicts. When there are no interests, conflicts just end up forgotten and nobody cares, but that's not good either.

So my take on "should the rest of the world interfere" is - yes, but only if the rest of the world does so by agreement.