In this chapter, we describe a causal analysis of a single historical story, the acquisition of the Panama Canal Zone by the United States. The causal analysis has two aspects. 'First, it is an assumption about the mental representations that are constructed as part of story understanding. Second, it is a methodological tool by which one can assess the parts of the story that a given individual has understood or recalled. We do not independently demonstrate that the kind of structure we describe is, in fact, a mental representation. Rather we assume that it is, drawing on empirical demonstrations that causal structures of this general kind have some psychological status (Trabasso & van den Broek, 1985). It may turn out that some other representation form is a closer fit to some kinds of psychological data, and hence qualifies as a psychologically better model. Until such time as critical data are available, ours is a plausible working assumption about what it means to understand a history story as a causal-temporal structure.