Complex sentence: The army in the east, on the other hand, chose Probus; the two met in battle, and when it was clear Probus had the superior force, Florianus was assassinated by his own troops.
Split into simpler sentences: The army in the east, on the other hand, chose Probus. The two rival Emperors met in battle, and when it was clear Probus had the superior force, Florianus was assassinated by his own troops.