Certainly nothing that will ever occur in our time but I still find it an interesting concept. For one thing just think of what could be done with all that money we now spend either preparing for or recovering from wars. Syrians for instance would likely prefer to stay home rather than jumping into flimsy boats to escape the bombs from the Russians and their own government.
Well the thing with governments is that they need to be stable to be effective, and legitimate and representative. Even strong gov institutions can't prevent civil wars. Look at the USA. So i don't think a world gov would stop war, you'd just might have less country-to-country war but still civil wars.