Are civil wars shaped by how they start? While existing literature points to the path-dependent nature of conflict, the link between the type of onset and wartime dynamics have been largely overlooked. Building on a recent typology capturing the dynamics of civil war onset (1944–2020), I analyze conflict trajectories, focusing on three macro-level wartime dynamics: warfare, intensity, and duration. This article shows that how large-scale armed conflicts begin (e.g., whether they start as peripheral conflicts or are fought centrally) helps us predict how intensely they will be fought or how long they will last. These findings show that onset matters beyond signaling the start of large-scale conflict and tells us about the dynamics that will likely follow. Altogether, this article establishes a new process-oriented macro-level research program in the field of conflict analysis.