Peter Turchin’s research while affiliated with University of Oxford and other places

Scholars from a wide array of disciplines have sought to identify the core features underpinning cohesion and cooperation within increasingly large, complex, and internally diverse societies. Previous work has suggested that as societies grow in scale and complexity, extreme forms of inequality no longer provide a viable method of maintaining cohesion and cooperation. The relationship between these supposedly critical features, however, has not been subjected to large-scale systematic analysis. Here, we investigate the rise, spread, and impact of cooperation-promoting institutions and ideologies in a global sample of past societies. We find a clear divergence in the evolutionary trajectories of these traits: on one hand, certain ideological features relating to the adoption of moralizing religions, increasing complexity and professionalization of governmental administration, and maintenance of public goods clearly arise and spread alongside increases in social scale; on the other, ideologies and institutions limiting rulers’ power and authority are not uniformly characteristic of larger-scale societies. We discuss a range of possible interpretations for these patterns, noting that the forces driving these developments may operate on different scales of analysis and time-courses and suggest tentative explanations for these critical dynamics.

Soil fertility depletion presents a negative feedback mechanism that could have impacted early adopters of agriculture. We consider whether such feedback can lead to population cycles among early agriculturalists, such as the boom-and-bust patterns suggested by an increasing amount of evidence for Neolithic Europe. Using general mathematical arguments, we show that this is unlikely, due to the interplay of two factors. First, there is an important mathematical difference between biotic (i.e., logistic) and abiotic resource replenishment; soil nutrients are better modeled by the abiotic case, which leads to more stable dynamics. Second, under realistic conditions, the resource replenishment process operates on fast time scales compared to attainable population growth rates, reinforcing the tendency towards stable dynamics. Both these factors are relevant for early agricultural societies and imply that nutrient depletion is likely not the main contributing factor to boom-and-bust cycles observed in the archaeological record.

As the concept of polycrisis gains popularity among academics, policy-makers, and the general public, many questions linger about the utility, scope, and applicability of the term in different contexts. Building on prior work, we argue that crises can fruitfully be understood as existing along a spectrum, characterized by multiple different factors, with our modern polycrisis at one extreme. We illustrate this by surveying three historical periods with varying geographical scope – late 1st-millennium CE Mesoamerica, Late Medieval Eurasia, and the early modern Northern Hemisphere – arguing that these exhibited many, but not all, of the key characteristics that make up a polycrisis. We detail the experience of individual societies during these periods, focused on regions to highlight how stresses and dysfunction across multiple systems combined to produce devastating impacts and contrast these with the relatively mild experiences of others facing the same conditions. We highlight how the interaction of stresses across ecological, economic, social, and political systems produced disasters that further deepened these crises and so led to yet more disasters and further devastation. We illustrate how viewing these historical periods through a polycrisis lens can not only inform our understanding of the past but can produce valuable lessons for our modern world. The multi-faceted, far-reaching, and devastating consequences of our current polycrisis should not be viewed as entirely a recent phenomenon. Ultimately, we argue that studying historical polycrises as we do here can help us learn lessons from the past that allow us to hone strategies for addressing the comparable issues we face today and will continue to contend with for the foreseeable future.

The impact of inter-group conflict on population dynamics has long been debated, especially for prehistoric and non-state societies. In this work, we consider that beyond direct battle casualties, conflicts can also create a ‘landscape of fear’ in which many non-combatants near theatres of conflict abandon their homes and migrate away. This process causes population decline in the abandoned regions and increased stress on local resources in better-protected areas that are targeted by refugees. By applying analytical and computational modelling, we demonstrate that these indirect effects of conflict are sufficient to produce substantial, long-term population boom-and-bust patterns in non-state societies, such as the case of Mid-Holocene Europe. We also demonstrate that greater availability of defensible locations act to protect and maintain the supply of combatants, increasing the permanence of the landscape of fear and the likelihood of endemic warfare.

A first horizon scan on tipping points in global catastrophic risks.

The scientific understanding of the complex dynamics of global history – from the rise and spread of states to their declines and falls, from their peaceful interactions with economic or diplomatic exchanges to violent confrontations – requires, at its core, a consistent and explicit encoding of historical political entities, their locations, extents and durations. Numerous attempts have been made to produce digital geographical compendia of polities with different time depths and resolutions. Most have been limited in scope and many of the more comprehensive geospatial datasets must either be licensed or are stored in proprietary formats, making access for scholarly analysis difficult. To address these issues we have developed Cliopatria, a comprehensive open-source geospatial dataset of worldwide states, political groups, events, and rulers from 3400BCE to 2024CE. Presently it comprises over 1800 political entities sampled at varying timesteps and spatial scales. Here, we discuss its construction, its scope, and its current limitations.

Societal ‘crises’ are periods of turmoil and destabilization in socio-cultural, political, economic, and other systems, often accompanied by varying amounts of violence and sometimes significant changes in social structure. The extensive literature analyzing societal crises has concentrated on relatively few historical examples (large-scale events such the fall of the Roman Empire or the French and Russian Revolutions) emphasizing different aspects of these events as potential causes or consistent effects. To investigate crises and prior approaches to explaining them, and to avoid a potential small-sample size bias present in several previous studies, we sought to uniformly characterize a substantial collection of historical crises, spanning millennia, from the prehistoric to post-industrial, and afflicting a wide range of polities in diverse global regions; the Crisis Database (CrisisDB). Here, we describe this dataset which comprises 168 crises suggested by historians and characterized by a number of significant 'consequences' (such as civil war, epidemics, or loss of population) including also institutional and cultural reforms (for example improved sufferance or constitutional changes) that might occur during and immediately following the crisis period. Our analyses show that the consequences experienced by each crisis is highly variable. The outcomes themselves are uncorrelated with one another and, overall, the set of consequences is largely unpredictable when compared to other large-scale properties of society suggested by previous scholars such as its territorial size, religion, administrative size, or historical recency. We conclude that there is no ‘typical’ societal crisis of the past, but crisis situations can take a variety of different directions. We offer some suggestions on the forces that might drive these varying consequences for exploration in future work.

In this article we respond to three critiques of our 2019 article ‘Complex Societies Precede Moralizing Gods throughout World History.’ We clarify that our research does not, as our critics suppose, support the claim that moralizing gods played a decisive role in the development of complex societies. Indeed our goal was to test this claim and we found it wanting. Our methods ‘reduce’ neither religion or social complexity in the ways claimed, while our tentative conclusions about the relationship between frequent, routinized ritual and social cohesion are supported by much research beyond the paper under discussion. In the Roman Empire, many forms of collective ritual contributed to the propagation of Romanitas. We have never claimed that this depended on absolute uniformity of belief. Other misconceptions about our supposedly ‘inattentive’ qualitative analysis result from misreadings of information in our open-access database, which functions as an evolving set of information relevant to specific research questions rather than a general encyclopedia. Despite these disagreements, we continue to maintain that neither qualitative historical methods nor quantitative analytic approaches alone can produce satisfying answers to causal questions about world history. The best approach, we argue, is to integrate the insights from humanities with ‘Big Data’ analyses from social science, and we welcome continued engagement and collaboration across traditional disciplinary boundaries.