It was in 1929, as the Great Depression loomed, that the American sociologist Warren Thompson first suggested that populations evolve via a set of uniform stages we now call ‘demographic transition’. The idea is a staggeringly simple one that can be easily assimilated by GCSE geography students. In every nation, mortality at first falls, leading to rapid population growth. Subsequently, fertility declines to bring the birth and death rates back into equilibrium. The idea can be illustrated in a mere two lines. As simple as the notion is, the consequences of demographic transition for societies are momentous, for population size and composition in terms of age, gender and the like are prime determinants of any society’s wellbeing.

Paul Morland’s The Human Tide traces the relationship between demographic change and social, political and economic transformations across the world over the past two centuries. The opening claim is bold – ‘There has been a revolution of population … over the last two hundred years or so, and that revolution has changed the world’ – but Morland’s scholarly instincts lead him to avoid the headline-grabbing simplifications beloved of publishers. Take his interesting account of the role of demography in the First World War. It starts with a grandiose flourish: ‘what ultimately mattered was not superiority of courage, technology or strategy but sheer weight of numbers.’ British population growth was slowing, with Germany enjoying a higher rate of reproduction. Germans in turn were anxious about the still-faster demographic expansion of the Russian giant to the east. All this is true, and Morland can point to much contemporary journalism, scholarship and political rhetoric about demography being destiny. Yet none of this means that numbers were the most important factor in determining the outcome of the Great War. Morland knows this and acknowledges as much as his narrative unfolds, coming to the conclusion that ‘the factor of population’ was ‘inextricable from other aspects of rivalry’. 

After dealing with the First World War, Morland traces demographic transitions in Europe and North America in the interwar decades, before moving on to the period after the Second World War. He notes that in the developing world the transition has tended to become ever more rapid over time. He