‘They breed like rabbits’ said the Reverend Ian Paisley, ‘and multiply like vermin.’ The occasion was a loyalist rally in 1969; ‘they’, of course, were Catholics. As political tensions in Northern Ireland erupted into the Troubles in the late 1960s, the fundamentalist preacher Paisley attributed the blame squarely to Catholics and their high birth rate. Northern Ireland’s very existence, separate from the Republic of Ireland, and the ideology of unionism that gave it support, was bound up with the idea that it was a ‘Protestant state’; but by the 1960s the Catholic population was growing. Many Protestants saw this growth in numbers as a threat, and Paisley gained his notoriety (in part) by expressing and exploiting this feeling. In one infamous speech to an enraged crowd in the Protestant-majority Shankill area, he revealed the addresses of some of the area’s new Catholic inhabitants; violence was the predictable outcome.

Unquestionably, Paisley was extreme; but more moderate unionists often accepted (some more grudgingly than others) the demographic element of his analysis. ‘The basic fear of Protestants in Northern Ireland is that they will be outbred by the Roman Catholics’, admitted Terence O’Neill, the moderate who served as Northern Ireland’s most consequential Prime Minister in the 1960s.

Many—both within the province and without—see the demographic divide between Catholics and Protestants as the key to understanding Northern Ireland. As a survey article of Irish demographics puts it, there is a somewhat ‘macabre interest’ in religious demography in Northern Ireland, and ‘percentages and ratios, which elsewhere would attract little general attention, are never far from the surface in political discourse’.

A look at some basic facts suggests ‘very’. Even the shape of Northern Ireland is based on demography. Founded by Protestant political leaders during the Irish War of Independence, who were fearful of ‘Rome rule’ from a new parliament in Dublin run by southern Catholics, Northern Ireland’s boundaries were drawn up with the explicit aim of creating a two-to-one Protestant majority. At the 1926 census, the first after the war ended, Catholics made up only 35.5% of the province’s population.

But the long-term stability of the Protestant majority was uncertain from the beginning: for almost the entirety of the past century, Northern Ireland’s Catholics have had a higher birth rate than their Protestant counterparts. Differences in birth rates between Protestants and Catholics is hardly unique to Northern Ireland, but the province’s dual demographics are exceptionally clean. Its Protestant and Catholic populations both underwent a very archetypal demographic transition; it just so happened that these occurred many decades apart from each other (sixty to eighty years, according to one estimate).

The Protestant majority was relatively stable for the first forty years or so of Northern Irish history, because a higher Catholic birth rate was offset by higher rates of Catholic emigration; 60% of Northern Irish emigrants before the Troubles were Catholic. However, entering into the 1960s, Catholic emigration fell, and the balance of population began to shift: by 1971, the Catholic population had grown to about 40%.

As the Troubles rolled on, Catholic Northerners continued to have more children than their Protestant counterparts. And with a minor baby boom after the peace agreement in 1998, the shift in the province’s demographics has continued apace, especially as the Protestant population has declined in absolute terms. Despite their traditional dominance of Northern Irish politics, since the 2017 election unionist parties (largely supported by Protestants) have been a minority in the Northern Ireland Assembly; and a century after the establishment of Northern Ireland as a Protestant state, the 2021 census showed Catholics outnumbering Protestants for the first time. With Sinn Féin today the largest party in the Assembly, it seems that the demographic fears of Paisley have become a reality; many are already suggesting that a united Ireland is now inevitable.

This narrative, of demographic changes leading to political shifts, is compelling on the face of it. And the basic fact underlying it—that Catholic fertility has been consistently higher than Protestant fertility for a long time—is undeniable. But when we peek beneath the surface, complications begin to emerge.

We can start with the attribution of the Troubles to demographic changes: while attractive, this explanation is difficult to square with broader quantitative evidence. Large-scale, cross-country analyses have generally failed to find any connection between the relative proportions of ethnic or religious groups in a country (or the rate of change of these proportions) and the probability of ethnic conflict in that country.

And ultimately, it’s not clear that any explanation for the Troubles in terms of religious demography is necessary. The basic cause of rising unrest was a new baby-boom generation of educated and politically-engaged Catholic youths, who rebelled against the perceived complacency of their established political leaders and engaged in bolder and more direct action, culminating in the late 1960s. But remove the word ‘Catholic’ from that last sentence, and I could be talking about nearly any Western country—France, certainly, West Germany, even the United States. In this regard, at least, the Northern Irish experience was anything but special: groups such as NICRA even explicitly modelled themselves on the American Civil Rights Movement in their fight against discrimination, with ‘We Shall Overcome’ becoming the unofficial protest anthem. The rise of Catholic radicalism was of a piece with events happening throughout the Western world in the late 1960s; the addition of a demographic element to the analysis—one which fails to fit the broader data—is unhelpful at best, misleading at worst.

What was relatively unique about Northern Ireland, however, was that its elites violently repressed these 1960s movements in a way that rapidly led to a breakdown in political order and the beginning of an armed insurgency. Those who believe in the power of religious demographics have tended to focus on this phenomenon—Protestant repression, rather than Catholic radicalism—in their explanations of the Troubles.

A representative version of this argument can be seen in the work of Eric Kaufmann. According to Kaufmann, Northern Irish elites ‘inclined’ towards anti-Catholic discrimination in order to keep Catholic emigration rates high: it was, at least partly, a strategic attempt to offset high Catholic fertility. Catholic emigration dropped off in the 1960s only because the central government in London—never quite understanding all this fuss about religion—pressured Northern Irish leaders to expand the province’s welfare state for all citizens. This meant that, when Catholics began to demand more general anti-discrimination reforms in the 1960s, it was at precisely the time when Protestant elites’ project of demographic management had broken down, producing fear and resentment that led to the reactive and violent actions of police and politicians towards Catholic protestors. Particular pressure for repression came from the Protestant-only Orange Order, which dominated unionist politics and which was strongest in areas where Protestants were in the minority: increasing numbers of Catholics fuelled their fear, and thus their desire to repress Catholic protests. And before long, ‘Protestant repression fuelled Catholic support for the IRA, and hence violence’: the Troubles. As global quantitative analyses suggest, demographic change did not directly cause conflict; but in Northern Ireland, Kaufmann and others have argued it played a crucial role.

Again, this story can seem compelling; but it deserves scrutiny, especially when it draws a connection between discrimination and emigration. While Northern Catholics emigrated much more than Northern Protestants, the disparity is not so stark when we compare them with Southern Catholics, who were also leaving Ireland in droves before the 1960s (at a rate much higher than the small number of Southern Protestants).

Rather, anti-Catholic discrimination flowed from the ideology of Northern unionism, which historically included a view of Catholics as a subversive fifth column seeking to undermine the existence of Northern Ireland. In the decades after 1921, ‘disloyal’ came to be used as a de facto synonym for ‘Catholic’, and unionist politicians openly boasted about discriminating against those disloyal to the Protestant state. As Northern Ireland’s economy deindustrialised and stagnated after the First World War,

The steady drip of demographic change only ever means anything if it is imbued with meaning by politics and culture: high Catholic fertility rates led to discrimination and repression only because elites identified Catholicism with disloyalty. Likewise, the growth in Catholic numbers helped propel the violent Irish nationalism of the Provisional IRA only because many Catholics, who by and large had been only weakly in favour of (or sometimes even indifferent towards) a united Ireland before the 1970s, came to see unification with the South as increasingly necessary—even as they gained demographic strength within Northern Ireland. Conflicts like the Troubles are almost never just a brute clash between religious or ethnic groups, driven by nothing more than pure tribalism; they are fuelled by conflicting political ideas. These political variables, which can rarely be readily explained by demographic factors, are what we really need to understand.

This is even more true when we turn to modern-day Northern Ireland; for while the Catholic demographic transition happened decades later than the Protestant one, it has happened. My own family structure bears this out: while my grandparents had absurd numbers of siblings, coming from stereotypically massive Catholic families, both my parents have three siblings, and I have only two. Catholics still tend to have more children than Protestants, but their fertility has shrunk as the economic fortunes of Catholics have caught up with Protestants (overt discrimination is largely a thing of the past), and as the cultural and social influence of the Church—whose opposition to contraception and attitudes towards female education contributed to high fertility— has declined.

The decline in Catholic fertility has tempered the change in demographics: between 2011 and 2021, the Catholic or Catholic background share of the Northern Irish population increased by only 0.6 percentage points (from 45.1% to 45.7%). And indeed, the share of the vote given to Irish nationalist parties in Northern Ireland Assembly elections did not increase significantly over this period (it was just over 41% in 2011, and about 40% in 2022).

As I’ve argued elsewhere, a far more consequential shift in the last decade of Northern Irish politics than the seeming success of Sinn Féin has been the rise of the so-called ‘other’ grouping: those political parties representing neither unionism nor Irish nationalism. In particular, the Alliance Party (a social liberal party which is officially neutral on a united Ireland) more than doubled its seat count in 2022 to become the third-largest party, winning 13.5% of the vote—up from 7.7% in 2011, and only 3.7% back in 2003. This has largely been driven by the affluent and by young people, groups of voters who increasingly feel disconnected from the traditional political and religious categories. Increasingly, people have begun to feel that their political goals and projects can’t be captured by either political tradition, unionism or Irish nationalism.

This change is not happening symmetrically, however: the rise of the ‘others’ has eaten much more into the Protestant population than the Catholic one. Unionism is on the decline politically, with unionist parties receiving 40% of the vote in 2022 compared to nearly 47% in 2011, due in no small part to the success of the Alliance Party in affluent Protestant areas. Indeed, Alliance is much stronger east of the River Bann (a traditional dividing line between Catholic-heavy and Protestant-heavy regions), and has struggled with candidate quality in Catholic-heavy areas. And, especially in response to Brexit, more people (especially young people) from a Protestant background are identifying themselves as ‘Irish’ as well as (or instead of) ‘British’ or ‘Northern Irish’.

Some of this is being driven by secularisation, which is happening in a lopsided manner in Northern Ireland. Of those who said they had no religion in 2011, a majority identified as British, and over two-thirds identified either as British or Northern Irish; only 14% thought of themselves as Irish compared to 28.4% of the general population, which suggests that those from a Protestant background are secularising more quickly than their Catholic counterparts. Or at least, secularisation in Catholic communities had less of an impact on cultural identity and political beliefs.

The traditional link between religion and politics in Northern Ireland has never been completely solid. Before the Troubles Irish nationalism was a relatively weak political force even among Catholics—former SDLP leader John Hume once famously quipped that ‘you can’t eat a flag’. Catholics in Northern Ireland never reached the levels of unanimity in their support for Irish unification that Protestants traditionally have in their opposition to it. And today, that Protestant unanimity is breaking down as the politics of ‘other’ emerges, a process that is being accelerated by secularisation and the breakdown of a simple Catholic / Protestant religious dichotomy. These political and cultural developments, much more than Catholic birth rates, are what matter in today's Northern Ireland.

As demographic shifts have slowed, political developments—which can happen on a shorter timescale than ‘across many decades’—have begun to overtake them. In Northern Ireland, the basic demographic fact of higher Catholic fertility is unchanged, but the assumptions that were habitually made about how this would translate into social and political outcomes have not been borne out. What we have in Northern Ireland is not demographics driving politics—indeed, it’s politics driving demographics, as political shifts and secularisation begin to enter into population statistics, and census data starts to show a decline in Protestant and British identity.

If a united Ireland comes in the short or medium-term future, it will be the result not of high Catholic fertility but of the rise of the ‘others’, who will be more willing and able to engage in bargaining and horse-trading with Irish nationalists over the issue than unionists have been. And if it doesn’t come, it will be because unionism was able to establish a renewed sense of political leadership and offer a more attractive settlement, or because the province simply muddled through, with its leaders keeping their heads down and ignoring difficult constitutional questions. None of these events will be the result of high Catholic fertility, just as the events that gave us the Troubles were to a large degree separate from demographic considerations. Demographics can matter, but they are never fundamental.

The reason that they are not fundamental is that they are entangled with politics and culture. This is true not just in the basic sense that policies and wider culture can affect birth, death, and migration rates; more fundamentally, the variables we care about in demographics (religion, language, ethnicity) are political and cultural variables, and the correlations that govern them are not laws of nature but products of politics. Protestant faith, unionist politics, and British identity have been tightly correlated for almost all of Northern Ireland’s history, as have (to a lesser degree) Catholic faith, nationalist politics, and Irish identity. But these correlations were not handed down from on high in 1921: they are the result of the province’s political and religious culture, which is far from stable. Whatever trends or tendencies are discovered by demographers, they can only be relied upon if we hold the political and cultural background fixed—not always a reasonable assumption.

Indeed, the times when people are most frantically searching for explanations or predictions, and hit upon demographics as the supposed key—those tend to be moments of crisis and change, exactly the times when culture and politics are most dynamic and unstable. When you base your assumptions about the future on large-scale statistical trends, you find that they have a tendency to collapse right at the moment when you need them most (especially with the operations of Goodhart’s law). Northern Ireland’s future is uncertain and unstable, but whatever it is will be determined in the voting booth and around the negotiation table—not in the maternity ward.

Peter McLaughlin is an independent researcher with a focus on intellectual history who holds a BA and an MPhil from the University of Cambridge. He writes at Her Fingers Bloomed.