US's military power is too strong. Russia is in such a bad shape that it can't even win Ukraine. China never goes to any war; their equipments suck as we saw in the Venezuela occurrence.
Nobody is going to help Iran. China and Russia only see Iran as the enemy of my enemy. Other than that, Chineses and Russians are likely disgusted by Iran's culture e.g. how they treat women. It would be like wtf why are we helping people like this?
The world will continue being policed by US and Europe.