The following statements correctly define factors that contributed to the decline of the Roman Empire:
- Incompetent rulers placed huge tax burdens on the Roman citizens.
- A long period of peace throughout the empire led to a sense of overconfidence in Rome.
- Rome could not grow enough food and maintain a large enough army to fend off barbarian tribes.
The statement about the empire splitting into three separate units ruled by a consul is incorrect; the Roman Empire was divided into different regions and later split into the Western and Eastern Roman Empires, but not ruled by consuls in the manner suggested.