News this week that China has introduced a three-child policy pricked up my ears. It says it wants to reduce its old-age dependency ratio — and fair enough. But is it possible that strategic competition in the 21st century will enter a new dimension: population size?

China has a hefty lead on the United States in population. That matters because it is fast catching up in terms of income per capita. Once the two nations are closer in economic development, population size will determine strategic heft.

Meanwhile, in America, author Matthew Yglesias has written a provocative book titled One Billion Americans in which he demands a trebling in the size of America — in part to help keep China at bay.

“We want America to stay number one,” he said.

Pity the poor planet if population becomes a strategic battlefield.