Julius Ceasar was a man of many talents. He was well educated, excellent speaker and a military genius. He earned prestige from the soldiers as a result of a new practice of paying soldiers with gold and land, not only for the good of the Republic. On the other hand, he also increased popularity within the common people after his many successful military campaigns.
He raises to power after allying with another general Pompey and a wealthy Patrician, Crassus. They took control of the Roman Republic and Ceasar was thrust in the position of Consul. Later on, this triumvirate broke down, with the death of Crassus and the consequent defeat of Pompey, who fought against Caesar. He made himself dictator and absolute ruler of Rome.
But his faith changed, after an attempt to become lifetime dictator. He asked the Senate to follow his asking which resulted in a plot to end his life. The senators succeeded in ending his life, and at the same time, ended the Republic.
As we can see, the best answer will be D, Ongoing conflict and threats of invasion made his military skill appealing.