According to Zeihan, China, and to a lesser extent India, have a horrible demographics problem looming. The prediction was for a dramatic collapse in manufacturing capacity. China at least might have the central authority to kill all those too old to work or consume, but my understanding is that doesn't fit well with the predominant culture there which highly respects age. Also, the whole killing people thing...

All the nations, especially those that industrialized quickly are facing this problem. As industrialization correlates strongly with smaller families (don't need children to work the farm). But China compounded it with the one child policy. And they industrialized faster than almost anyone. India went straight for a service economy, that may be even worse. Russia... Not sure about Brazil.

The US delayed its demographic collapse via immigration. It might even effect a soft landing relative to the rest of the world if it can ramp back up manufacturing in a way that doesn't destroy shared resources or enforce permanent underclasses leading to revolt. That isn't an easy task.