It sounds nice, but let's think about a few things first.

1. Humans are selfish and will fight to keep what is theirs.

That means that if people, Kim Jong Un for instance, didn't see enough in it for them, no deal. And even if enough (if any) governments were able to merge together, Kim Jong Un and whoever else would just consider the unified nation an enemy in all likelihood.

2. In the past, unification required force and bloodshed.

China's Three Kingdoms, the American civil war, Napoleon, Hitler, The Romans, the Greeks, the Babylonians... all were examples that unifying everyone under one government, for better or worse, is often easiest to accomplish through bloodshed and force.

This is why I see no hope for world peace, or at least that even though it is a nice ideal, the effort may not be worth it.