Simple Global Economics
The world is dependent on the US economy because it is the biggest consumer of goods and services. Because the US economy is competitive, it also engenders innovation. Even China's economy us buoyed by American consumerism. If the US economy were to become third world (as in Socialism), the rest of the economies would similarly devolve, because the countries will have no healthy market to sell their goods and services. Even China would collapse as a nation, a country that is not even able to feed its own people. Then, the world will also revert to old-time imperialism to bolster the economies that will be drastically reduced because of the absence of a strong market. So, for those countries that want to destroy the US, be careful what you ask for. Power must be wielded with wisdom; otherwise, those who wield it might just be cutting its own legs.