From the archive · July 25, 2026
When a rising power meets a ruling one
Why do a rising power and a ruling power so often end up at war?
01 · Word
Hegemon
noun
A state powerful enough to dominate its region or era and set the rules the other states follow
Examples
Sparta entered the war as the acknowledged hegemon of the Peloponnese, the large southern peninsula of Greece, and the rise of Athens threatened that standing.
Analysts still argue whether a rising power can overtake a reigning hegemon without a war.
Origin
From Greek hēgemōn, “leader” or “guide,” from hēgeisthai, “to lead.” Greek writers used hegemonia for leadership of an alliance of city-states: Sparta held it over the Peloponnesian League, while Athens turned a naval league into an empire under its own leadership.
02 · Idea
The Thucydides Trap
When a rising power threatens to displace a ruling one, both sides begin making fear-driven choices, and the structural stress between them makes war far more likely, even when neither side wants it.
Political scientist Graham Allison coined the term, drawing on Thucydides' judgment about Athens and Sparta. Reviewing the past five hundred years, his Harvard team identified sixteen cases in which a rising power challenged a ruling one; twelve ended in war.
No single insult or incident makes the war. The rise itself does, and the fear it inspires.
Structural stress does not pull the trigger; it loads the situation so that ordinary crises can become causes of war.
Limits and context
The sixteen-case tally is contested, with critics questioning which cases count and how they are coded. Four of the cases avoided war. Allison's own point is that the trap is a tendency to manage, not a law of history.
Thucydides never wrote the word “trap.” The modern label compresses his one-sentence diagnosis of 431 BC into a warning aimed at today's rising and ruling powers.
03 · Moment
The growth of Athens, the fear of Sparta
Athens and Sparta; the Peloponnesian War begins in 431 BC
In 431 BC the Greek world's two leading powers went to war for twenty-seven years. Thucydides, an Athenian general who lived through it, looked past the official grievances and named the deeper cause: the growth of Athenian power, and the alarm it inspired in Sparta.
- Rivals
- Athens & Sparta
- War begins
- 431 BC
- Chronicler
- Thucydides
The caveat
Thucydides wrote as a participant, an Athenian general exiled mid-war, and he reconstructed speeches from memory and report. His “truest cause” is a historian's interpretation, stated once, not a proven law of politics.
In his history he wrote that “the growth of the power of Athens, and the alarm which this inspired in Lacedaemon, made war inevitable.” Sparta ultimately won in 404 BC, but the long war exhausted both powers and ended the golden age of classical Greece.
Lacedaemon is the ancient name for the Spartan state; “Sparta” names its chief city.