Abstract
<jats:title>Abstract</jats:title><jats:p>When do leaders fear that a revolution elsewhere will spread to their own polities, and what are the international effects of this fear? This book develops and tests the domestic contagion effects theory. According to the theory, fear of contagion is driven more by the characteristics of the host rather than by the activities of the infecting agents. In other words, leaders will fear revolutionary contagion when they have significant revolutionary opposition movements that share the same ideological affinity of the revolution. Whether the revolutionary state merely serves as a model for revolution or whether it also acts as a platform, attempting to spread revolution abroad, is not the crucial distinction. When leaders have a fear of contagion, it will have a profound effect on international politics, prompting hostility toward the revolutionary state and cooperation with states that have similar fears, sometimes in contrast to geopolitical pressures. Cases spanning the reaction to the democratic American Revolution and the Dutch Patriot Revolt, the wave of liberal revolutions in Europe in 1820–21, the Russian communist and Italian fascist revolutions, and the Iranian Islamist revolution in the Middle East largely, though not uniformly, support the theory. This book advances our understanding of when, why, and how much states with different domestic ideologies affect international relations. In certain periods in international relations, one simply cannot make sense of international politics—patterns of alliances and wars—without considering the fear of contagion.</jats:p>