This study employs comparative process tracing to examine both the absence and onset of insurgency across four U.S.-led regime change occupations: Germany, Japan, Afghanistan, and Iraq. Existing literature on civil conflict has not employed such systematic comparison of post-conflict environments to analyze state stability. This work considers multiple variables, including economic conditions and ethnic grievances in the target states, but also introduces a novel variable termed “regime co-optation” – the process of incorporating a former regime into the post-conflict socio-political framework. Each case study is carefully examined before all four occupations are juxtaposed to test the various causal factors and hypotheses. Ultimately, economic instability and ethnic grievances do not consistently catalyze insurgency. The research instead finds strong evidence that regime co-optation is a centrally important variable in ensuring post-conflict state stability.