“The growth of the power of Athens, and the alarm which this inspired in Lacedaemon, made war inevitable.”Thucydides · History of the Peloponnesian War
Great wars arise from the fear of a rising power against an established one, not merely from hatred.
Thucydides explained the outbreak of war between Athens and Sparta through deep fear: Sparta, the older power, grew afraid of Athens's rapid rise. That fear pushed both sides toward conflict, even though neither truly wanted it at first. Historians today call this pattern the Thucydides Trap.
Why it matters Analysts still use this idea today to discuss rivalry between today's great powers.