Complex sentence: When Demosthenes wanted to renew the war after Philip went into Phocis, Eubulus and his supporter argued for peace, but from 344 BC on, Eubulus'influence was waning, and by 342 BC, Demosthenes' party was in control.
Split into simpler sentences: When Demosthenes wanted to renew the war after Philip went into Phocis, Eubulus and his supporters argued for peace. But from 344 BC on, Eubulus'influence was waning, and by 342 BC, Demosthenes' party was in control.