"China's rise doesn't necessarily imply the United States' decline. This is because if both countries trade, then both benefit from specialisation that raises efficiency. The problem is of course some people and industries lose, while others win — so the key is the distributional effects from trade as opposed to the overall economy gaining. Of course, there will be areas where the countries are competitors and both have been known to raise barriers in their markets which are problematic."

http://www.bbc.co.uk/news/business-23456018