The turmoil in Eurasian continent and Population explosion in Africa when you compared to improved peace in Americas. I will bet by shirt on Americas in general and USA in particular. No, Sir China is not going to touch US in military terms during my life time and probably have some economic benchmarks they may dominate but per-capita will suck. For all the hew and cry, China is middle-income nation with 17 neighbors, Middle East even with Petro-dollars in basket case, Europe is demographically falling and struggling with Immigration.
America will remain the power to reckon for next 50 years if not more.