In his book The Peloponnesian War, Thucydides explains that the war started because Sparta saw Athens as a threat to its hegemony. In this talk Jiang Xueqin argues that the American scientist James Calhoun’s “rat utopia” experiments offer a better explanation. In the 1950s and 1960s James Calhoun conducted experiments in which colonies of rats were put into worlds of plenty and abundance. All these experiments ended in disaster. Rather than enjoying paradise, the rats violently fought amongst themselves, and their social order collapsed. Why did this happen? In a wealthy world, high-status rats could live longer, which meant younger rats had no opportunities to achieve status. Consumed by anxiety and anger, this younger generation became violent and destructive. Fifth-century Athens was a “rat utopia.” After Persia was defeated in 479 BCE, Athens established the Delian League, and it became a de facto empire. The upper nobility was happy with the status quo, but the lower nobility clamored for opportunities to achieve fame and fortune. Athens became expansionist and imperial to ease its internal contradictions, and this ultimately led to the outbreak of the Peloponnesian War.