You seem to underestimate the power of nationalism as a uniting force. China for decades has instilled in its citizens the imagery of the sleeping giant who has been ignored/exploited/abused by other world powers and that is now due its rightful turn on the world stage. If you don't think nationalism is a potent force just look at how Putin or Trump have created fervent followers - it's not through any other clever unifying principles.

I also grow tired of hearing how a shrinking birth rate causes vast demographic challenges for a country, when that stance is not balanced with the acknowledgement that a growing population also creates vast demographic challenges, and (as we are seeing worldwide) toxic consequences for the entire planet. It's just that we are more familiar with the pressures and problems created by population growth, even as we fail to adequately address them .