During WWII, Germany, Italy, and Japan formed the Axis powers.
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history
轴心国 ('Axis powers') comes from Mussolini's 1936 metaphor of a 'Rome - Berlin axis' (罗马 - 柏林轴心), later extended to include Tokyo. Today the term is also used loosely in geopolitics - e.g. former US president George W. Bush's 邪恶轴心 ('axis of evil').