From Asia Times:
The biggest factor determining global stability over the next 20 years, simply put, is China. For good or bad, it will shape the world. If everything goes well, China will be integrated in the developed world and will become one of its engines, if not the main engine. If things go bad, there could be a confrontation that makes the Cold War pale in comparison.
All other scenarios are in between these two extremes, including the collapse of China or a war led by the United States. This latter could sap all US forces and energies, thus killing with one stone China and the US and allowing the emergence of a third power.