Relationships by Country

East Asia

Begin where the wave has traveled furthest. More than half the countries on Earth, holding a clear majority of the world’s people, now have fertility below the level that replaces a generation, and the line keeps moving outward. East Asia is where it has moved farthest and fastest. South Korea, Japan, Taiwan, and China have pushed their birth rates to the lowest ever recorded in peacetime, and they did it inside a single lifetime: the same retreat from marriage and childbearing the West went through, run at higher speed and against a harder economy.

One caution belongs at the very start, because it shapes every comparison in this essay. Fertility, marriage, and cohabitation are counted differently from one country to the next, and a “marriage” or a “birth outside marriage” does not mean quite the same thing in Seoul, Bogotá, and Lagos. The figures here are directional. They are close enough to line the regions up and see the shape of the thing, not precise enough to rank two similar countries by a tenth of a point.

The worry itself is not new. The oldest surviving version of it was written more than two thousand years ago, by a Greek historian watching his own country empty out.

The mechanism he named, children traded away for status and ease, is the one modern surveys still turn up when they ask people why they stopped at one child, or none. What has changed since Polybius is the scale. He was describing a few Greek cities. The same arithmetic now runs almost everywhere.

The reasons are by now familiar, because they are a sharper version of the West’s. Housing in Seoul, Tokyo, and the big Chinese cities is priced beyond a young couple’s reach. Education has become an arms race that starts before kindergarten and swallows a family’s savings. Women have gained schooling, careers, and independence far faster than the domestic bargain around them has changed — so marriage still tends to mean a second shift of housework and childcare landing on the wife. The culture kept asking for a fully funded, traditionally organized marriage long after the economy that once supported one had gone.

Because marriage and birth stay so tightly tied here, the collapse of marriage in China reads straight through to its birth rate — and the register that records weddings tells that story plainly.

It is tempting to lay China’s decline at the door of the one-child policy, and the timing rules that out. Chinese fertility began dropping in 1970, nine years before the policy arrived, falling from nearly six children per woman to under three across that decade under an earlier campaign to marry later and space births out. By the time the one-child rule was written into law, the steep part of the fall had already happened, as Our World in Data has documented at length. The policy took the credit, and later the blame, for a curve already in motion — the official lever moving only after the trend had set, a sequence that repeats across almost every country here.

The texture behind the numbers is easier to feel than to measure. Younger Koreans talk, in the press and in surveys, about giving up on dating, marriage, and children as a single package, a widely reported shorthand for a generation that increasingly treats partnering as a cost it cannot afford. The exact share who feel that way is hard to pin down and easy to sensationalize, so the survey numbers here are worth treating with real caution.

Latin America

Latin America runs the experiment in almost the opposite order and arrives at the same place. Marriage here never held the monopoly it holds in East Asia. Across much of the continent, couples have for generations formed households, raised children, and stayed together without ever registering a wedding — the unión libre, the free union, a socially accepted arrangement with roots that run back centuries. Sex, cohabitation, and childbearing were only ever loosely tied to the certificate. And fertility fell below replacement all the same.

The fertility figures tell the same story.

So the region that decoupled marriage from childbearing longest ago still followed everyone else down to low fertility. A relaxed attitude to the wedding certificate bought it no extra children.

South Asia

India poses a harder question: what happens to the birth rate when the old marriage system does not loosen at all? Marriage in India remains close to universal and, for most people, arranged. Families still vet and select partners, weigh caste and community and dowry, and broker the match; the couple’s own preference has grown but still sits inside a decision the two families largely make together. This is the alliance model the companion essay described — alive and load-bearing in the world’s most populous country. And underneath it, the birth rate has quietly slipped past the line.

And it reached that point without the marriage revolution the West and East Asia went through first.

So India has reached a below-replacement birth rate with its marriage institutions still standing. That combination is what makes it such a useful test.

Two things complicate the picture. Some urban surveys report arranged marriage falling fast among the young, but many of them draw on wedding-industry or big-city samples that skew toward exactly the couples most likely to have chosen each other, so the national picture is almost certainly more traditional than a fashionable metro dataset suggests. And South Asia is not a single story: Pakistan and Bangladesh sit at their own different points, on their own paths, and the Indian figures above should not be read as standing in for the whole region.

Middle East & North Africa

No country has fallen faster than Iran, and none makes the point more sharply, because Iran spent decades trying, with the full weight of the state, to steer its birth rate: first up, then down, then up again — and lost the wheel every time.

The sequence is close to a controlled experiment. During the war with Iraq in the 1980s the revolutionary state wanted soldiers and encouraged large families, and Ayatollah Khomeini spoke of raising an army of twenty million. When the war ended the government reversed itself completely: a family-planning programme relaunched at the end of the 1980s, contraception was made free and, crucially, sanctioned by clerical fatwa, and the message became ‘Fewer children, a better life.’ Fertility then fell through the floor. Alarmed at how far it had dropped, Supreme Leader Ali Khamenei reversed course once more, calling in 2011 for a population of 150 million and ordering a fresh pronatalist push. The birth rate barely responded.

The retreat from childbearing shows up just as plainly in the retreat from the wedding itself.

Iran is the extreme case, and it is not a lonely one. Next door, Turkey (a very different country, secular in its state and long oriented toward Europe) recorded a fertility rate of 1.48 in 2024, its eleventh straight annual decline and a record low, despite a government that has pushed hard for three children per family. Across the wider Middle East and North Africa the regional average still sits well above replacement, held up by higher-fertility countries elsewhere in the region. But its two demographic heavyweights on the northern rim, one a Shia theocracy and one a secular republic, have both fallen well below replacement.

The rest of the region is more mixed than Iran and Turkey alone can show, and the honest position is not to overreach. The wealthy Gulf states and the countries of North Africa sit at their own various levels, some still well above replacement, and their trajectories deserve more than a sentence borrowed from Tehran. What is clear is the direction of travel, which everywhere in the region points the same way: later marriage, smaller families, and a widening gap between what the culture expects and what the demography delivers.

Sub-Saharan Africa

End where the wave has barely arrived. Sub-Saharan Africa holds the highest fertility on Earth and the youngest populations, and it is the one large region where marriage, children, and kinship still look roughly as they did across most of human history: early and near-universal marriage, bride-wealth passing between families, and, in a wide belt across the middle of the continent, polygyny that is still openly and widely practiced.

Even here, though, the ground is shifting. Fertility has begun to slide across much of the region as girls stay in school longer and cities grow — and one measure catches the change with unusual clarity.

One rich country cuts hard against the whole pattern. Israel’s total fertility rate is 2.79 (UN WPP 2024), the developed world’s lone above-replacement outlier and close to double the OECD average of roughly 1.5, and its fertility stays high across income and education levels, running above every other rich country’s rate even among secular Israelis. Israel kept something the rest of the wealthy world let go of — the one strong hint that the decline is not quite a law of nature.

The evidence across sub-Saharan Africa is thinner than for any other region here, and these claims should be held most loosely. Trends in child marriage, the current prevalence of polygyny, and the wide gap between city and countryside are all moving and unevenly measured, and the region’s data are far thinner than East Asia’s or Europe’s. What can be said is modest and probably durable: the plateau is real, it is beginning to tilt, and the coming decades will test here what has already played out most everywhere else.

Across the five regions, a single shape resolves. The mandatory-marriage societies and the optional-marriage ones, the theocracies and the secular republics, the arranged-marriage heartland and the free-union continent have all arrived, or are arriving, at the same low-fertility destination by roads that could hardly look more different. Polybius saw the mechanism clearly enough two thousand years ago — comfort and status crowding out children. He simply saw it early, in a handful of Greek cities, when it would take another two millennia to reach the rest of us. His was a lament for a few towns. This is most of the species.