Final answer:
Mussolini was removed from office in 1943 because of military defeats that led to a loss of confidence and a vote by the Grand Fascist Council to remove him.
Step-by-step explanation:
Benito Mussolini was removed from office in 1943 primarily due to military defeats Italy faced during World War II. Italy suffered major setbacks on various fronts, including the invasion of the Soviet Union, where half of the 200,000 Italian troops sent became casualties. The Allied victories in North Africa and Sicily and the Allied bombing of Rome in July 1943 significantly weakened Mussolini position and humiliated his regime.
A government was formed under Marshal Pietro Badoglio, who commenced secret negotiations with the Allies. This led to Italy's surrender in September, shortly after which Mussolini was rescued by German forces. Nonetheless, Mussolini's removal was irreversible and marked the end of his reign as Italy's fascist leader.