Which factors caused the decline of the Roman Empire? Select all correct answers.

A. Waves of smallpox, plague, and other diseases brought to Rome from foreign lands ravaged the city.

B. Locally hired soldiers guarding the frontiers tended to support their own commanders over leaders in Rome.

C. Julius Caesar's defeat by Carthage in the Third Punic War cost Rome most of its overseas possessions.

D. Sending Romans overseas as soldiers left fewer farmers near Rome and led to severe food shortages.