Answer: Caesar became the sole ruler of the Roman Empire by waging civil war against his political opponents and taking the throne.
Explanation: In order to gain more power, Caesar leaves Rome to command the Roman army in Gaul (France), where he had several victories. Caesar's popularity and legend began to grow and Pompey rightly feared Caesar's legions as they were personally loyal to Caesar rather than to the state. Pompey convinced the senate to order Caesar to relinquish command and return home without his army. Caesar refused to give up command but instead chose to march his entire army home to take control of Rome.
After this episode, Caesar became the undisputed master of Rome and he pursued reforms that strengthened his power. He provided land pensions for his soldiers and restructured the debts of a significant percentage of Rome's debtors.