Honestly nevermind the nukes, the US is the current hegemonic power, the dollar the current hegemonic currency. Some countries might be starting to break away from the dollar, but basically all the countries powerful enough to act against America still have their economies intertwined with America's, so they would be tanking their own economies by doing so. Even China would suffer massive economic damage from destroying America currently. Even without the threat of nukes it would be difficult to convince people to make the necessary sacrifices to their quality of life.