There is no marauding military force marching behind a modern-day Hitler, nor will the question be put to a vote by a 'league' of nations.
Global governance is completely incompatible with national sovereignty.
A world army, under the command of the the UN Secretary General, is the final step in centralizing the enforcement power. The U.S. Constitution is a major obstacle on the road to global governance. The process is inefficient. But that's how it's supposed to be. But the process eliminates much imprudence and produces the best policies human minds are capable of producing at the time.