See? That's the Federation working with a non-Federation civilization put an end to a conflict hands on. No "it's none of our business" or "Let's see if they survive the night".
But if you force a solution on someone that they really don't want, then that solution isn't likely too last for long. I agree with Picard that the only way a lasting solution would be reached would be to hold the Angosian governments feet to the fire.
And Peter David postulated that Eminiar and Vendikarr went to war anyway and Vendikarr was obliterated in DC Comics (2nd run) issue #11, "...Let's Kill All The Lawyers!"