Complex sentence: During the 1920s, the Socialist Party was a leading left-wing political party that was close to the Tudeh Party of Iran and it joined the Tudeh-led United Front of Progressive Parties in 1946, effectively absorbed by the larger group.
Split into simpler sentences: During the 1920s, the Socialist Party was a leading left-wing political party. Close to the Tudeh Party of Iran it joined the Tudeh-led United Front of Progressive Parties in 1946 and was effectively absorbed by the larger group.