Complex sentence: By now, Rome had also sent a force under Valerius Flaccus, to apprehend Sulla and deal with Mithradates, which passed through Macedonia, crossed the Hellespont and landed in Asia, where many of the Greek cities were in rebellion against Mithridates.
Split into simpler sentences: By now, Rome had also sent a force under Valerius Flaccus, to apprehend Sulla and deal with Mithridates. Flaccus' army passed through Macedonia, crossed the Hellespont and landed in Asia, where many of the Greek cities were in rebellion against Mithridates.