There have been many causes: a decade of war in the greater Middle East, with its enormous cost in “blood and treasure”; the financial and economic crisis; high public debt; reorientation toward internal problems; and a new focus on Pacific affairs. Add to this America’s relative decline in view of China’s ascendance and that of other large emerging countries.
无论从主观还是客观方面，美国都不愿也不能再发挥这样的作用。个中原因非常复杂：比如说付出巨大“生命和财产”代价的十年大中东战争；金融经济危机；巨额公共债务；调整定位转向国内问题；以及太平洋事务成为新的焦点。此外还有相对于中国和其他新兴大国崛起的美国相对衰落问题。