This study focuses on sources of uncertainty in two substantive areas of international security: militarized disputes and economic sanctions. We revisit realist and liberal debates as two long-standing paradigmatic approaches that address the role of uncertainty, and draw on their insights to identify key variables that represent sources of uncertainty. We evaluate these variables’ effects on uncertainty using a heteroskedastic probit model and data on disputes and sanctions. We find that measures of power parity, system multipolarity, joint democracy and trade are significantly linked to levels of uncertainty for disputes and military conflict. For sanctions, only realist variables affect uncertainty levels. We also find some evidence of a substitution effect suggesting that factors that increase the likelihood of military conflict and the amount of uncertainty about military options tend to have the opposite effect when it comes to sanctions.