Final answer:
The division of the Roman Empire into eastern and western halves did not contribute to the end of the Pax Romana in the 3rd century AD.
Step-by-step explanation:
The three factors that contributed to the end of the Pax Romana in the 3rd century AD were a 20-year plague weakening the Roman army and demoralizing the civilian population, barbarian invasions causing widespread destruction and loss of life in several Roman provinces, and frequent revolts by units of the Roman army leading to the murder of many Roman emperors. However, the division of the empire into eastern and western halves by two rival emperors did not directly contribute to the end of the Pax Romana.