Economic power (and that also buys you political influence) comes from the size of the economy. The size of the economy enables military power.
China (and India) have 4x the US' population. China's land area is the same as the US'. It's simply a matter of time for them to be more powerful economically than the US, and then it's really up to them to also topple the US militarily.
Which, unless blimps take over soon, will be until the advent of the space elevator.