Complex sentence: Class Zero go to Milites for the signing of a peace treaty, and during their time there, Machina learns that Class Zero are responsible for Izana's death, and that he was planted in Class Zero by Rubrum's government to spy on Arecia.
Split into simpler sentences: Class Zero go to Milites for the signing of a peace treaty. During their time there, Machina learns that Class Zero are responsible for Izana's death, and that he was planted in Class Zero by Rubrum's government to spy on Arecia.