In his analysis of the Peloponnesian War, Thucydides uses a single Greek word, kindunos, an extraordinary two hundred times, often with contorted grammatical and syntactical constructions which focus his reader's attention on its use. With the assumption that Thucydides is writing for a retrospective reader who understands the outcome of the war as well as many of the smaller episodes which led to that outcome, the problem is to determine exactly why Thucydides relies so heavily on this word, particularly in instances when any number of simpler words or constructions would have provided a more straightforward explanation. To solve this problem, this dissertation examines Thucydides' use of the term kindunos, not on a case-by-case basis as in a commentary, but on a thematic basis by constructing broad categories that help explain one aspect of Thucydides' purpose. This dissertation shows that Thucydides uses the term kindunos in different ways in order to express to his reader the idea that there are two forms of danger threatening his contemporary world: external dangers and internally generated ones. The external dangers are the more easily defined. Thucydides' era was filled with strife and his analysis is of a twenty-seven year long war between Greek poleis. The internal dangers, however, are harder for modern readers to define as they are a result of Thucydides' contemporaries' tendency to give into internal urges: the urge to act, to preserve honor, to exact revenge, and to intervene on others' behalf. This dissertation uses Greek tragic poetry, contemporary to Thucydides' writing, to help define these emotional urges. It also relies heavily on interstate relations theories, namely the Realist paradigm, to define the mechanics of inter-polis behavior Thucydides witnessed. But, in the end, this dissertation argues that Thucydides' didactic message to his reader was that in an already dangerous world there is only one way for leaders to hope to mitigate the danger: they must eschew emotional urges and respond to external situations with rationality and reason instead.