Choosing Sides: The Dynamics of Coalitions

2006年秋天，逊尼派部落与伊拉克的基地组织结盟，并与美国结盟。这沿着美国军队的激增和美国战略的改变扭转了叛乱的进程。结盟决策和联盟动态往往是决定内战和国家间战争结果的关键因素。然而，在过去二十年里，关于战争的原因和行为的理论研究很少涉及联盟。这项工作取得了非常重要的见解。但它几乎完全集中在两个演员的模型。在此基础上，该项目试图将来自战争的两个角色模型的见解扩展到制定和分析联盟。其中包括第三方决定是否以及如何干预消耗战;第三方在代理战争中的作用;分而治之的一般模式，以及在接近目标时倾向于打破联盟的向心力。这一项目的一个主要成果将是为估计第三方干预内战的影响的经验性努力提供更明确的概念基础。展望该项目的更广泛影响，联合国难民事务高级专员公署最近报告说，2014年有近6000万流离失所者，其中一半是儿童（纽约时报，2015年6月18日）。内战是主要原因。更清楚地了解联盟动态可能是减轻这些影响的一小步。结盟决策和联盟动态通常是决定内战和国家间战争结果的关键因素。然而，自费伦的《战争的博弈论解释》（1995）发表以来的20年里，关于战争原因和战争行为的正式的博弈论研究主要集中在两个行动者的博弈上，通常是两个行动者的讨价还价博弈。这项工作在联盟问题上基本保持沉默。在此文献的基础上，该项目试图将来自战争的两个角色模型的见解扩展到冲突阴影下的模型联盟动态的制定和分析。更具体地说，这个项目的目标是识别和分析联盟形成中的广泛的、典型的问题，然后将它们形式化为“主力”模型。初步工作已经分析了第三方在决定是否在消耗战中偏袒哪一方时所面临的问题。两个角色的消耗战通常用于模拟许多不同类型的冲突，包括内战。消耗战被认为是全薪、第二价格拍卖，它被推广到允许n个玩家竞争n-k个奖品（Bulow和Klemper，1999）。然而，令人惊讶的是，以前没有人分析过一个非常自然的问题，即当第三方对谁赢得消耗战有偏好，并且可以通过支持一方或另一方来影响结果时，它会怎么做。本计画将首先延伸及概括消耗战选边模式分析的初步结果。然后，该项目将阐述其他联盟问题，例如分而治之（或统治），以及当联盟接近目标时往往会分裂的向心力。

In the fall of 2006 Sunni tribes turned on Al Qaeda in Iraq and allied with the United States. This - along with the surge in American troops and a change in American strategy - reversed the course of the insurgency. Alignment decisions and coalition dynamics are often key factors in determining the outcome of civil and interstate wars. Yet theoretical work done over the last two decades on the causes and conduct war of has very little to say about coalitions. This work has made very important insights. But it has almost exclusively focused on two-actor models. Building on that literature, this project attempts to extend the insights derived from two-actor models of war to the formulation and analysis coalitions. These include a third party's decision of whether and how to intervene in a war of attrition; the role of third parties in proxy wars; a general model of divide and conquer, and the centripetal forces that tend to break coalitions apart as they near their goals. A main result of this project will be a clearer conceptual foundation for empirical efforts to estimate the effects of third-party intervention in civil wars. Looking to the broader impacts of the project, the United Nations High Commission for Refugees recently reported that there were nearly 60 million displaced people in 2014, half of them children (New York Times, 18 June 2015). Civil war was a major cause. A clearer understanding of coalition dynamics may be a small step toward mitigating these effects.Alignment decisions and coalition dynamics are often key factors in determining the outcome of civil and interstate wars. Yet the formal, game-theoretic work done on the causes and conduct of war in the twenty years since Fearon's "Rationalist Explanations of War" (1995) has largely focused on two-actor games, often on two-actor bargaining games. This work is largely silent on coalitional issues. Building on that literature, this project attempts to extend the insights derived from two-actor models of war to the formulation and analysis of models coalitional dynamics in the shadow of conflict. More specifically, the goal of this project is to identify and analyze broad, canonical problems in coalition formation and then formalize them as "workhorse" models. Preliminary work has already analyzed the problem facing a third party in deciding whether to take sides in a war of attrition. Two-actor wars of attrition are commonly used to model many different kinds of conflict, including civil wars. Thought of as all-pay, second-price auctions, wars of attrition have been generalized to allow for n players competing for n-k prizes (Bulow and Klemper 1999). Surprisingly, however, no one has previously analyzed the very natural question of what a third party would do when it has preferences over who wins the war of attrition and can influence that outcome by supporting one side or the other. This project will first extend and generalize the preliminary results of the analysis of the model of choosing sides in a war of attrition. The project will then formulate other coalitional problems like divide and conquer (or rule), and the centripetal forces that tend to break coalitions apart as they near their goals.