Complex sentence: After the war, Simon Sabiani joined the SFIO in 1919, and also for a while the PCF.He then founded in 1923 the "Parti d’action socialiste", (Socialist action party).
Split into simpler sentences: After the war, he joined the SFIO in 1919, and for a while the PCF. In 1923, he founded the "Parti d’action socialiste", (Socialist action party).