We discuss models and data of crowd disasters, crime, terrorism, war and disease spreading to show that conventional recipes, such as deterrence strategies, are often not effective and sufficient to contain them. Many common approaches do not provide a good picture of the actual system behavior, because they neglect feedback loops, instabilities and cascade effects. The complex and often counter-intuitive behavior of social systems and their macro-level collective dynamics can be better understood by means of complexity science. We highlight that a suitable system design and management can help to stop undesirable cascade effects and to enable favorable kinds of self-organization in the system. In such a way, complexity science can help to save human lives.

There have been more than 200 wars since the start of the 20th century, leading to about 35 million battle deaths. However, efforts at forecasting conflicts have so far performed poorly for lack of fine-grained and comprehensive measures of geopolitical tensions. In this article, a weekly risk index is derived by analyzing a comprehensive dataset of historical newspaper articles over the past century. News reports have the advantage of conveying information about contemporaries' interpretation of events and not having to rely on meaning inferred a posteriori with the benefit of hindsight. I applied this new index to a dataset of all wars within and between countries recorded since 1900, and found that the number of conflict-related news items increases dramatically prior to the onset of conflict. Using only information available at the time, the onset of a war within the next few months could be predicted with up to 85% confidence and predictions significantly improved upon existing methods both in terms of binary predictions (as measured by the area under the curve) and calibration (measured by the Brier score). Predictions also extend well before the onset of war-more than one year prior to interstate wars, and six months prior to civil wars-giving policymakers significant additional warning time.

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Students of international relations have long argued that large and rapid shifts in relative power can lead to war. But then why does the rising state not alleviate the concerns of the declining one by reducing its expected future power, so that a commitment problem never emerges? For example, states often limit their ability to launch preemptive attacks by creating demilitarized zones, or they abandon armament programs to avoid preventive wars. In a model of complete information, I show that shifts in power never lead to war when countries can negotiate over the determinants of their power. If war occurs, then, it must be that negotiations over power are impossible or too costly. I then show how third parties, domestic politics, and problems of fungibility can increase the costs of such negotiations, and hence lead to war, even under complete information.Keywords: conflict; causes of war; bargaining; power; war; power shifts Students of international relations have long argued that rapid shifts in relative power can lead to war. 'The growth of Athenian power and the fear which this caused in Sparta' or the rise of Germany, for example, are common explanations for the Peloponnesian war and World War I, respectively.1 More recently, the economic and military rise of China has led many to wonder about the likelihood of a war with its neighbors or the United States. 2 In each case, the declining state fears that it will negotiate in a position of weakness once the balance of power has shifted, 1 The quote is from Thucydides (1984). The rise of Germany as a cause for World War I is discussed in Joll (1992), and with a twist, in Ferguson (1999, 83): 'The key to the arms race before 1914 is that one side lost it, or believed that it was losing it. It was this belief which persuaded its leaders to gamble on war before they fell too far behind'. See also Ferguson (2006). 2 See, for example, Hoge (2004), Bijian (2005), or Mearsheimer (2006. 228terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org/10.1017/S175297191100008XDownloaded from https:/www.cambridge.org/core. University of Basel Library, on 11 Jul 2017 at 17:31:41, subject to the Cambridge Core and hence it is argued, prefers fighting now. The problem is not that there are no peaceful solutions that both parties would prefer to war; the costs and risks of war ensure that there always exists such an agreement. 3 Rather, fighting occurs because any commitment to a specific course of action once the balance of power has shifted is inherently non-credible. This line of argument, however, is problematic. If indeed rapid changes in relative power lead to inefficient conflicts, then why do states not negotiate over the causes and speed of this shift. In other words, why would the rising state not offer today concessions of capabilities that reduce his expected power tomorrow? Abandoning a weapons program or withdrawing troops from the border, for example, are simple ways to alter expected incentives in the next period, and hence to credi...

Explaining the emergence and stability of cooperation has been a central challenge in biology, economics and sociology. Unfortunately, the mechanisms known to promote it either require elaborate strategies or hold only under restrictive conditions. Here, we report the emergence, survival, and frequent domination of cooperation in a world characterized by selfishness and a strong temptation to defect, when individuals can accumulate wealth. In particular, we study games with local adaptation such as the prisoner's dilemma, to which we add heterogeneity in payoffs. In our model, agents accumulate wealth and invest some of it in their interactions. The larger the investment, the more can potentially be gained or lost, so that present gains affect future payoffs. We find that cooperation survives for a far wider range of parameters than without wealth accumulation and, even more strikingly, that it often dominates defection. This is in stark contrast to the traditional evolutionary prisoner's dilemma in particular, in which cooperation rarely survives and almost never thrives. With the inequality we introduce, on the contrary, cooperators do better than defectors, even without any strategic behavior or exogenously imposed strategies. These results have important consequences for our understanding of the type of social and economic arrangements that are optimal and efficient.