The Intrusion Factor: Insurrection and the Effects of Foreign Military Intervention

Why do foreign military interventions in support of counterinsurgents fail to consistently secure outright victory for their clients? In this thesis, I seek to clarify the effects of foreign military intervention (FMI) on intrastate conflict processes and outcomes. I test the plausibility of the theory that foreign intrusion produces a number of political and strategic effects that impede counterinsurgency. Specifically, I argue that FMI generates acute nationalist and populist resentment and resistance, and undermines the legitimacy of the regime it supports while increasing popular support for the insurrection. FMI also exacerbates information problems and creates incentives for foreign forces to resort to barbarism. This leads to indiscriminate violence by foreign forces, which further alienates the population. FMI can also alter the strategic dynamics of a conflict in ways that undermine the chances of government outright victory.Following a review of the extant literature on insurrection and foreign intervention, I propose a framework for illustrating the strategic dynamics between belligerents’ capabilities and strategies over time. I then conduct a mixed-methods study on the effects of FMI using a newly synthesized dataset of 263 cases of intrastate war. I test the relationship between FMI and the odds of supported governments defeating their insurrections outright and find that FMI has no statistically significant effect on conflict outcomes in a bivariate test, or when controlling for other variables. I then examine the case of the U.S. intervention in South Vietnam as a crucial case of FMI, and find strong support for the causal mechanisms of the intrusion factor theory.