The Unitary Socialist Party (PSU) was a social democratic political party in Italy that was active from 1922 to 1930. The party was founded by Giacomo Matteotti and Filippo Turati after they, along with other members of the reformist wing of the Italian Socialist Party, were expelled. In 1924, Matteotti was assassinated by the National Fascist Party, leading to the "Aventine Secession", in which the Socialists left Parliament, thus allowing for the fascists to establish a single-party state. The PSU was outlawed in 1925 and operated clandestinely until 1930, when it rejoined the PSI.
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