The Peloponnesian War, according to Thucydides, was set off by a pretext that should be peculiarly familiar to us. Its background was not so different from that of modern wars. The conflict had its roots in the growing power of Athens, which came to be regarded as a threat to the safety of its neighbors. The Corinthians were among those most anxious to declare war on Athens before it was too late. To do so with any hope of success, however, they needed the superior strength of the Lacedaemonians, whose main city was Sparta. The Lacedaemonians had also become restive but were bound by an agreement to maintain a truce with Athens for thirty years.
The immediate issue for the Corinthians was whether to come to the aid of Potidaea, which was both a Corinthian colony and a tributary ally of Athens. Afraid of a revolt by Potidaea that would set off revolts by other Athenian allies, Athens took preventive action to forestall a Potidaean uprising. Athens’ action was thus an effort to prevent its dominoes from falling.
In retaliation, the Potidaeans backed by the Corinthians sent envoys to Lacedaemon to seek support against Athens. When the Lacedaemonians promised support, Potidaea and other tributary cities staged their revolts. Corinth soon sent a considerable force to the aid of Potidaea. Yet the great war between Sparta and Athens had not yet broken out. To settle the issue, the Lacedaemonians called a congress of their allies, most of whom wanted to break the truce and declare war on Athens and its allies. At the congress the main argument in favor of war was made by the Corinthians. Their argument was probably the first fully recorded case of a policy based on falling dominoes.
The Corinthian argument turned on the issue of supporting Potidaea, now besieged by the Ionians, who were themselves dependent allies of Athens. If we think of Potidaea, which was not itself worth going to war for, as somewhat akin to Korea or Vietnam in contemporary history, we have a rough modern equivalent.
The Corinthians were forced to admit that assisting Potidaea was “quite a reversal of the order of things.” They justified it on the ground that all were threatened by “the tyrant city that has been established in Hellas,” driven by “a program of universal empire, part fulfilled, part in contemplation.” It was, they urged, “impossible for us to wait any longer when waiting can only mean immediate disaster for some of us.” Since all were potential dominoes, the Corinthians argued, they might as well challenge the expansionist Athenians in Potidaea, despite the distance and difficulties. As for Potidaea, it fell to the Athenians, who totally wiped it out—and Potidaea is never mentioned again.
Out of such rationalization came the disastrous Peloponnesian War. Thucydides set an example, from which all future historians could profit, of distinguishing between the real and the ostensible causes of this war. “The real cause I consider to be the one which …