In the sixteenth year of the Peloponnesian War, an Athenian expedition descended upon the small island of Melos, about 90 miles south of Athens in the Aegean Sea, and demanded that the Melians join in alliance or be destroyed. Although a Spartan colony, Melos had remained scrupulously neutral in the war. Her citizens, unwilling to renounce their independence, sought unsuccessfully to dissuade the Athenians from attacking them. The Athenians explained that an independent Melos situated in the very heart of the Athenian imperium encouraged other island allies to aspire toward independence. Their failure to put an end to the anomaly of Melian independence would therefore be seen by friend and foe alike as a sign of weakness on Athens' part.
The really intriguing question about the Melian dialogue is not the Athenian decision to invade Melos but rather Athenian toleration of Melian independence for the first sixteen years of the Peloponnesian War. For surely, if Melian independence constituted a threat to Athens in 416 B.C. it must have done so in 430 B.C., the year in which the war broke out, and in all of the years in between. Why then did Athens wait so long to impose its hegemony over the island? The answer, implicit in Thucydides' narrative history of the Peloponnesian War, contains an important insight into the nature of aggression, one, moreover, that is particularly germane to contemporary international relations.
The Athenian reply to the Melians stresses the subjective nature of power; if others think of you as powerful, you are powerful and vice versa. For this reason, states must be concerned about their image abroad and must from time to time offer vivid demonstrations of their capability and resolve. The Athenian invasion of Melos, unnecessary for any strategic reason, was envisaged as such a display.