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Why did Italy join Germany in World War II?

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World War II: Germany invading Poland — World War II Germany invading Poland, September 1, 1939.

Italy’s decision to join Germany in World War II was driven by a combination of diplomatic isolation, expansionist ambitions, and the constraints of a formal military alliance.

Following Italy's invasion of Ethiopia in 1935, the League of Nations imposed sanctions, which isolated Italy from Britain and France. Seeking support, Benito Mussolini moved into the orbit of Adolf Hitler, hoping German backing would force the Western powers to grant Italy further concessions. This relationship was formalized as the Rome-Berlin Axis in 1936 and solidified by the Pact of Steel in May 1939, a military alliance that committed both nations to support one another in conflict.

Although Mussolini initially remained neutral when Germany invaded Poland in September 1939, he feared losing his claim to conquered European territories as Hitler advanced. When France appeared on the verge of collapse in 1940, Mussolini, driven by opportunistic hopes for a quick victory, declared war on June 10, 1940.123