The Human Tide: How Population Shaped the Modern World. By Paul Morland.PublicAffairs; 352 pages; $28. John Murray; £25.

Empty Planet: The Shock of Global Population Decline. By Darrell Bricker and John Ibbitson.Crown; 304 pages; $26. Robinson; £20.

O NE CLUE to the character of a government comes from listening to what political leaders say about the national birth rate. Authoritarians such as Recep Tayyip Erdogan and Vladimir Putin tend to complain about it, and urge women to have more (or, occasionally, fewer) babies. Outright dictators like Josef Stalin and Nicolae Ceausescu believed they could actually alter it. Grumbling resignation, or silence, is a mark of liberal democracy.

In truth, governments can do little to change people’s minds about how many children to have. Even China’s one-child policy, introduced in 1979, probably only accelerated a drop in the birth rate that would have happened anyway. Two new books portray demographic change as an inexorable force that, rather than bending to leaders’ whims, steamrolls politicians and can change the course of history. They also suggest that what one of them calls “the great fairground ride of world population change” is running out of steam.

Many people have heard of Thomas Malthus, the 18th-century English cleric who predicted that human populations would grow faster than food production, leading to calamity. The American demographer Warren Thompson is less famous. But Thompson’s theory of demographic transition, which he outlined in 1929, has held up much better than Malthus’s prognostications. To begin with, Thompson observed, a country has a high birth rate and a high death rate. As farming and health care improve, mortality falls. The birth rate stays high for a while, then it begins to drop, too. Countries that have gone through this demographic transition have lower birth rates and lower death rates than they began with—and many more people.

During the journey, countries acquire and then shed particular strengths and frailties, owing to the changing size and shape of the population. A country in the second stage, with a high birth rate and a low death rate, is young and fast-growing. When the birth rate falls, too, the country enters a wonderful spell. With fewer children relative to the adult population, but still not many retirees to look after, it becomes a nation of able-bodied workers. Then it grows old.

Paul Morland’s “The Human Tide” is mostly about how this process has played out in Europe and Asia. Britain went first, to its great advantage. In the late 16th century England had 4m inhabitants—half as many as Spain, which helps explain why the prospect of a Spanish invasion was so terrifying. England’s population doubled by the early 19th century, then went bonkers. By 1901 England not only had 30m inhabitants; it had also disgorged many people across North America, Australasia and Africa. The country dominated partly through sheer weight of numbers.

The populations of Germany, Japan and Russia exploded a few decades later, causing others to worry (with some justification) that they too would try to grab more territory. Their swelling, young populations gave them clout at a time when war was largely a matter of flinging bodies at the enemy. The late 19th and early 20th centuries were an era of pro-natalism, and of fear that other countries were reproducing faster than one’s own. As a British newspaper put it in 1903: “The full nursery spells national and race dominance.”

That was never quite right, and seems even less true in the modern world of cruise missiles, international trade and soft power. But Mr Morland argues that demography continues to shape events. The Middle East, he writes, is unstable partly because it has so many young people. Japan no longer seems destined to be “number one”, as a book published in 1979 had it, because it has so few. Demography can heighten paranoia and resentment within countries, when one national or ethnic group appears to reproduce faster than another. The former Yugoslavia, where Serbs moved to a low birth rate before Bosnian Muslims or Kosovan Albanians, is “an exemplary case of the destabilising impact of uneven demographic transition”.

In the final stage of that transition, the birth rate falls below the death rate. That leads to population decline unless countries accept lots of immigrants. In “Empty Planet”, Darrell Bricker and John Ibbitson maintain that this is the fate of the entire world. As countries grow richer and more urban, and as more girls go to school, children cease to be economic assets. People begin to have babies not because they need them, or because village elders bully them into parenthood, but because they enjoy bringing them up. That desire can be satisfied with just one or two.

Mr Bricker and Mr Ibbitson regard a sub-replacement fertility rate (in which every woman has fewer than 2.1 children on average) as Europe’s “natural state”. They call the post-war baby boom a blip. Their book argues that even baby-rich sub-Saharan Africa will gravitate towards the one- or two-child norm faster than the sedate expectations of UN demographers. This may be right. The demographic transition seems to be accelerating: Asia and Latin America went through it more quickly than Europe. To mangle a phrase of Francis Fukuyama’s, the world could be heading for the end of demography and (eventually) the last man.

If so, it will reduce pressure on Earth’s resources. But perhaps the cheers should be muted. Shrinking populations are hard to manage: towns must be replanned and pensions trimmed. And many people in the rich world do not actually desire one or two children. Fully 41% of Americans think the ideal number is three or more. Most families fall short because relationships prove too fragile, houses too expensive, bosses too inflexible and conception too difficult. Behind that supposedly “natural” rate lies much disappointment.

As more and more countries go through the demographic transition, something else is becoming clear. The challenges and pitfalls of population change can be handled more or less adeptly. A bulge of young adults may have been a curse in the Arab world, but it was a blessing in China. Countries can adapt to an ageing population—by welcoming more immigrants and making it easier for mothers to do paid work—or they can stick their collective heads in the sand. Demography is a mighty force. It is not quite destiny.