We have to remember that world markets and economies are interconnected. Credit crisis was about some big companies failing and we witnessed turbulence in the world economy that is continuing until now. Now don’t say that China was not affected by the credit crisis. It in fact was affected. We can imagine what could befall the world economy if all of a sudden US collapse. It is a huge gap to be filled.
You logic is more apt in relation to US political power. Everyone knows that US uses economic power to further its political ambitions. The economic crisis and the series of wars have made US know that it is as mortal as any country is and would lead towards a multi-polar world sooner than expected.
The economic problems of the 3rd world are DIRECTLY caused by the US. They set up buyer's cartels and seller's cartels in a good boy's club that keeps 3rd world countries poor by setting up 2 near monopolies: 1 for buying raw materials at extremely low prices from 3rd world countries, and 1 for selling manufactured goods at extremely high prices to 3rd world countries.
That is why they are threatened by China and India. We broke their cartel. 3rd world countries can avoid selling to their cartels and sell directly to us. They can directly buy cheap manufactured goods (electronics, pharmaceuticals, etc) from us.However, we are still exploited by their cartels. For example, in textiles, the cartel made up of Nike, Adidas, etc. agree to simultaneously drop the price they will pay for original manufactured clothes; the factories don't have the branding or logistics power to sell the clothes themselves, so they are forced to pay the low price. In raw materials, they have a seller's cartel too; Rio Tinto leads the entire Australian ore industry and sets a high price for their ore that China can buy from nowhere else because Rio Tinto or its cartel mates control almost all the ore. At the same time, industry in China or India cannot afford to make buyer's cartels; China tried to make a buyer's cartel for its largest steel mills, but Rio just sold to smaller producers who cannot afford to wait instead.
So they make reverse cartels too: 1 for unified selling of raw materials (or at least the ones that they control, like iron ore), and 1 for unified buying of manufactured goods, aimed specifically at industrial 3rd world countries like China and India.
I'm not even talking politics and military, the US is extremely guilty in those fields, just economics.
The US and the West are basically like this:
There are 4 Asians and 1 white American stuck on a desert island.
The Asians gather food, build shelter, kill animals, make a fire, etc.
The white eats the food. He also cuts coconut tree leaves into "money" and exchanges these coconut leaves, for food and shelter.
Then the white tells the Asians: I am the sole driver of economic growth on this island. You can't kick me off, because if you do, you'll all be unemployed.
Do you see how ridiculous this is?