Complex sentence: The Marxist-leninist faction called the "terceristas" split into several groups the biggest of them went into the Movimiento Socialista Popular, while the rest went into the PSP.
Split into simpler sentences: The Marxist-Leninist faction, called the "terceristas", split into several groups. The biggest of them went into the Movimiento Socialista Popular, while the rest went into the PSP.