The number of divorces in England and Wales in 1857 - the last year in which divorce could be achieved only by decree of Parliament - was just five. With courts able to decree divorces, this had risen to an average of 215 per year in the period 1870-1874, to 590 per year in the period 1900-1904 and to 710 in the period 1910-1913. In short, until the First World War, divorce was virtually unheard of and confined to the rich.
The annual average for the four years immediately after the First World War was four times greater than immediately before it. The rise then settled down to a slower rate, reaching 4,000 by 1930, only to rocket again after the Second World War, stabilising at an average of 27,000 a year in the period 1952-1960.
In other words, there were already about 45 times more divorces in 1952 than at the start of the century. In the Sixties the number of divorces doubled, and it doubled again in the Seventies, and, in 1995, there were 165,000 divorces in England and Wales - 280 times more than in 1900. With different timing, similar trends occurred in Germany, in much of the rest of Europe and in the US, so this is obviously not just a British disease.
At the first level of explanation of this century-long trend are the reasons that divorcing couples themselves give. Like characters from situation comedies, the genders offer predictably different reasons.
Wives tend to cite physical violence, verbal abuse, financial problems, mental cruelty, drinking, neglect of home and children and a lack of love. Husbands are wont to cite parents-in-law and sexual incompatibility. However, most students of the subject treat these explanations as symptoms of deeper causes.
The next level consists of a series of conditions or antecedents that have been identified as correlating with divorced couples as opposed to intact couples and that include marrying young, marrying in a register office and being poor, among dozens of other factors.
But these are not necessarily explanatory in themselves. That register office weddings are less enduring, for example, is not caused by the ceremony in itself, but by the reduced commitment to the concept of marriage that such a ceremony is assumed to indicate - and, consequently, a greater reluctance to stick it out if the relationship sours.
The final level of explanation boils down to the effects of industrialisation and urban living. These are behind a range of factors such as rising expectations of what marriage can supply, liberalised divorce laws, increased numbers of working women, the decline of religion, improved education and welfare and reduced stigma as more people know divorcees and as the media reflects that trend.
It is from this list that most explanations for the rise in the second half of the century are drawn. The introduction in 1969 of "no-fault" divorce is often blamed for the rise, but the numbers had already doubled in the previous eight years - if anything, the new act was an effect rather than a cause.
None the less, one extremely influential aspect of the legislation was increased access to legal aid, which eased divorce for those on low incomes, particularly women. Changes to the rules of eligibility in 1914, 1920, 1949 and 1960 meant that, by 1966, one third of divorcees were from unskilled manual professions. Where once only the rich could afford divorce, now it was available to anyone - including women with no independent means.
The increased participation of women in the workplace was equally critical in making divorce a realistic financial plan. Where once a woman with a poor husband might have found herself with no income after a divorce, the fact that she could find work made her more confident about starting a new life.
Although there is no clear causal relationship, divorce and female employment are correlated. In 1980 in the US, for example, 50 per cent of married women worked whereas 75 per cent of those divorced did so.
Important, too, was the potential for gaining employment. In the Sixties and much of the Seventies, the easy availability of employment meant that, even if a woman were not actually employed, she felt confident of finding a job. Jobs may also have provided a psychological buttress - a protection against loneliness and isolation - and continuity during the separation and divorce process. On top of this, the newly established welfare state provided a safety net.
However, at least as significant was the change in values and morality. The stigma of divorce, which had been slowly eroded during the previous 75 years, seemed to collapse during the late Sixties and early Seventies. With the increasing tendency for people to live alone and apart from family networks, social controls and pressures to conform to moral edicts of older generations were eroded.
Taken together, all these changes meant that more people knew someone who was divorced, and it became more acceptable to have this status... so more people felt able to follow suit. As television tightened its grip on the public imagination and replaced radio as the main broadcast entertainment, it reflected the reduced stigma, in the process reinforcing the reduction.
At the same time there was a revolution in perceptions of the importance of relationships to happiness. The emotional content of marriage and deriving emotional fulfilment from it - the aspect of marriage which is, arguably, the most fragile - became unprecedentedly significant. The higher such expectations rose, the less they were likely to be fulfilled.
This change is linked by most analysts to the change in women's attitudes and expectations. Hardly a day goes by in the 90 per cent of the press that is right wing without one or other columnist (some of them divorcees or notorious extramarital philanderers themselves, and mostly men) lamenting the effect of feminism on modern marriage.
But it is not feminism as such that is to blame, it is the strain that modern life is placing on gender roles - as I shall explain next week.
Oliver James's book `Britain on the Couch - Why We're Unhappier Compared With 1950 Despite Being Richer' is now available in paperback, published by Arrow at pounds 7.99Reuse content