This is not apocalypse for highly populated countries like China and India. They have enough people who can replace current workers. They won't have a shortage

This is not apocalypse for highly populated countries like China and India. They have enough people who can replace current workers. They won't have a shortage in food production because the land exists and can be consolidated to fewer farmers. There is a surplus of hands still out there who can take up manufacturing. By the time China really faces mass declines like Japan, they will already have a significant portion of their economy transformed into a knowledge/information economy. In fact, a lowering population but increasing gdp will actually increase gdp per capita. The living people there will become richer per capita. For developed countries with already low populations, the story is different. Fewer hands means lesser manufacturing which means lower gdp and thus, lesser power in the global stage.