Explanations for the staggering transition from violence to peace in East Asia have primarily centred around domestic economic growth and political stability, economic integration and interdependence, stabilizing alliances and China as a regional hegemon (Tønnesson et al., 2013; Goldsmith, 2017; Ross, 2017; Scott, 2017; Tønnesson, 2017). In this paper, an argument is put forward that a benevolent demographic shift in China and East Asia, which to some extent stems from deliberate population policies, has supported economic and political development and contributed to a further deepening of the structural determinants of peace in the region.While earlier works addressing the political and economic consequences of demographic change have primarily focused on highly aggregate population properties like overall population growth, and often conclude that demographic factors have little impact, more nuanced works suggest that particular demographic developments affect both economic growth (Birdsall & Sinding, 2001) and political violence (Goldstone, 2010), though with variations depending on the context in which they take place. While often neglected in the discussion of the economic rise of the “Asian Tigers”, it is well-established that increasing demographic maturity in some of the key countries in the region (notably Japan, South Korea and, later, China and Vietnam), with a large, young and relatively well-educated labour force combined with fewer children, which in combination allow public investments to be shifted, is one important driver of the strong economic development and growth in export-oriented industry (Birdsall & Sinding, 2001). Hence, one cannot fully understand the “peace by trade” (Goldsmith, 2017) and the “peace by development” (Tønnesson, 2017) theses if the importance of the extensive demographic change in the region is ignored.The question posed in this chapter is, do recent demographic trends in East Asia support peace? Arguably, declining levels of violence in the region are associated with the two most pressing demographic challenges currently facing many East Asian[1] countries: a young age structure and a high level of urban population growth. In particular, the discussion of the importance of age structure transitions addresses both the potential security challenges related to “youth bulges”, and the “demographic bonus” argument pertaining to the potential economic boost provided by an increase in the labour force. A key intervening factor, human capital measured as age-specific education, is discussed.The chapter further addresses some more specific claims about potential security implications of sex-selective abortion and the resulting “excess males” in some countries, and the eventual population aging of the demographically maturing countries, arguably leading to concerns over different regional demographic trends and the ability to maintain welfare levels and military spending. However, while these latter emerging population developments will likely pose political and social challenges to countries in the region, it is less clear whether they may pose traditional security concerns. Rather, as the countries in East Asia continue to move toward lower fertility levels and smaller youth cohorts, we are likely to see a decline in conflict risk as countries move through the demographic transition. An aging population may arguably become more peaceful not only as a result of structural or material processes, but also as a result of a changing social mood. The chapter will discuss the possible mechanisms underpinning such a “geriatric peace” (Haas, 2007).In this chapter, peace is primarily understood relatively narrowly as the absence of armed conflict or other forms of political violence. However, current patterns of demographic change are also likely to affect the deepening of peace beyond the mere absence of war (Bjarnegård & Kreutz, 2017). Fewer children (and in China the rise of one-child families), could make parents more risk averse and perhaps even resentful of militarization. Aging populations could have a similar effect, as increasing shares of the electorate passes retirement age. Urbanization and expansion in education expose people to new ideas and have the potential to increase tolerance.The present study is restricted in important ways. First, demographic factors are rarely, if ever, the sole causal determinant of political violence. Typically, the relevance of demography depends chiefly on social, economic, political and ecological factors. While some key contextual factors are addressed, an extensive discussion is beyond the scope of the current project. Second, while the importance of demographic factors in violent revolutions has been discussed (Goldstone, 1991), recent studies of demographic change and political violence (e.g. Urdal, 2006) suggest that demographic factors appear to be more relevant for understanding low-intensity armed conflict than large-scale civil and interstate wars. Reference is also primarily made to the onset of such conflicts. Third, the current data structure only allows for systematic comparison across countries over time. However, country-level averages may mask very significant internal demographic variation, geographically as well as within sub-populations. Differential population dynamics between ethnic groups may be considered a potential security concern in its own right (Toft, 2007). Fourth, the current focus is on political violence, while certain forms of demographic change, particularly rapid urbanization and excess males, may equally well be associated with increased social violence and unrest. Melander (in this volume) shows that most East Asian countries score low on gender equality, which is reflected in the preference for sons and the resulting high levels of sex-selective abortion and excess males in countries like China, Vietnam and South Korea. As Bjarnegård (2017) notes, human security issues, some of which pertain to gendered relations, extend beyond armed conflict. Hudson and den Boer (2004) argue that skewed gender ratios may increase levels of interpersonal violence and prostitution. Finally, demographic factors are not exogenous to other aspects of development that also contribute to the East Asian Peace.