In a social network in which friendly and rival bilateral links can be formed, how do alliances between decision-makers form, and what determines whether a conflict will arise? We study a network formation game between ex-ante symmetric players in the laboratory to examine the dynamics of alliance formation and conflict evolution. A peaceful equilibrium yields the greatest social welfare, while a successful bullying attack transfers the victimized player’s resources evenly to the attackers at a cost. In within-subject and between-subject laboratory experiments, we find that the relative frequency of peaceful and bullying outcomes increases in the cost of attack. We further examine the dynamics leading to the final network and find that groups tend to coordinate quickly on a first target for attack, while the first attacker entails a non-negligible risk of successful counter-attack. These findings provide insights for understanding social dynamics in group coordination.

The rise of a new power may lead the dominant power to seek a preventive war. We study this scenario in an experimental two-stage bargaining game. In each stage, the rising power makes a bargaining offer and the declining power must choose whether to accept it or fight. Between the two stages, the winning probability shifts towards the rising power. We find fewer preventive wars when the power shift is smaller and when the rising state has the commitment power. Communication and repeated interaction decrease the likelihood of preventive wars. High fighting costs almost eliminate such wars when the rising power’s first-stage offer is sufficiently large.

We investigate how information about recipients’ characteristics affects donors’ giving as opposed to when no information is available. In a rational model in which information causes a donor to update her assessment of the recipient’s deservingness, we introduce the idea that altruism can be ‘persuadable’ (‘dissuadable’) by information about positive (negative) characteristics. We report data from three experiments in which donors are provided information regarding three recipient characteristics: alcoholism, attending courses, and disability. Across different characteristics, our results are broadly consistent with the predictions of persuadable altruism. Overall, we find a positive net impact of providing information on aggregate giving.

Communication is one of the most effective devices in promoting team cooperation. However, asymmetric communication sometimes breeds collusion and hurts team efficiency. Here, we present experimental evidence showing that excluding one member from team communication hurts team cooperation: the communicating partners collude in profit allocation against the excluded member, and the latter reacts by exerting less effort. Allowing the partners to reach out to the excluded member partially restore cooperation and fairness in profit allocation; but it does not stop the partners from talking behind the that member’s back even when they could have talked publicly. The partners sometimes game the system by tricking the excluded member into contributing but then grabbing all profits for themselves.

We study escalation and aggression in an experimental first-strike game in which two participants play multiple rounds of a money-earning task. In each round, both players can spend money to accumulate weapons. The player with more weapons can spend money to strike against the other player, which almost totally eliminates the victim’s earnings potential and removes their capacity to strike. Weapons can serve as a means of deterrence. In four treatments, we find that deterrence is strengthened if weapon stocking cannot be observed, that a balance of power is effective in maintaining peace, and that mutually beneficial trade decreases the risk of confrontation, but not necessarily the likelihood of costly arms races.