They have zero power. The US can destroy the UN in a flash. But in that instance, humanity would pay much more than extra bucks for shipping crap we don't need.

A strong AND fair UN is a good deterrent for world wars. Of course, it's better to renegotiate any precieved unfairness than to just blow all violence avoidance safeguards like a world congress.

China got away with their economic trickery because of US corporate greed and short sightedness combined with the US public insatiable consumerism. But we humans have a short memory and we like being empowered by bully leaders.

Let's just hope we'll survive this age without too much bloodshed.