THE PROSPECT of a relentlessly rising China that underlies the growing assertiveness of its Communist regime depends on years more of rapid economic expansion that, in turn, enables mounting financial and military clout. There are several reasons to doubt the inevitability of that progress, including the inherent brittleness of a political order increasingly dominated by a single ruler and dependent on systematic violations of human rights. But the simplest, and potentially most crippling, flaw in the “Chinese dream” of President Xi Jinping can be expressed mathematically: a rapidly shrinking birthrate. Already in decline for decades, China’s baby count has fallen by a third in the past five years, and its fertility rate is now one of the lowest in the world.

Though the slipping numbers are part of a global trend, China’s rulers greatly exacerbated the demographic reversal by imposing — and brutally enforcing — a limit of one child per couple beginning 40 years ago. The result was not only a lower population growth rate; China also now has a lopsided ratio of elderly to working-age people, and of men to women. Families are thinning out, along with the support networks they provide. The world’s largest cohort of single people is Chinese, and many of them are only-childs with little interest in raising children of their own.

Slowly and belatedly, the country’s rulers have tried to address this problem by loosening the limits on births. On Monday, Mr. Xi chaired a Politburo meeting that ratified an increase to three of the number of children allowed each family, along with a promise to invest more in education and child care. But the judgment of both demographers and average Chinese was swift: The reform was no more likely to succeed than the previous decision in 2015 to allow couples two children. In an online poll by the Xinhua news agency, 90 percent of 22,000 respondents said they would not even consider having three children. China’s censors then suppressed the results of the survey.

One reason the new policy won’t work is the regime’s insistence on continued control over women’s reproduction. Those who wish to have more than three children will still be banned from doing so. Disfavored minorities, including the Muslim Uyghurs, remain subject to forced abortions and other draconian measures to control population growth. High costs for housing, and limited options for child care, discourage childbearing among the urban middle classes.

The longer-term consequences of the trend are the subject of debate among demographers and economists. Some say a shrinking workforce population will eventually stunt the Chinese economy, limit the military’s manpower and force the regime to divert resources to the expanding portion of society that is over 65. Others suggest that the economy’s increasing productivity will more than make up for any decline in workers.

What seems clear is that the regime’s brutal attempts at social engineering — including millions of forced abortions and sterilizations — have complicated not just its aspirations to become the world’s dominant power, but also the long-term prospects for stability in the world’s most-populous country.

Read more: