How does battlefield activity affect belligerents’ behavior during wartime negotiations? While scholars have studied when and why warring parties choose to negotiate, few insights explain what negotiators do once seated at the table. I argue that actors engage in obstinate negotiation behavior to signal resolve when undergoing contentious and indeterminate hostilities. I explore this claim by analyzing all negotiation transcripts and associated daily military operations reports from the Korean War. Using text-based, machine learning, and statistical methods, I show that high levels of movement or casualties in isolation produce clear information on future trends, thus yielding more substantive negotiations, while more turbulent activity featuring high movement and casualties in tandem produces cynical negotiations. Moving past contemporary literature, this study explores micro-level dynamics of conflict and diplomacy, builds a theoretical bridge between two perennial views of negotiation, and provides a framework for studying war by applying computational methods to archival documents.