It consists of three books covering the events of 49–48 BC, from shortly before Caesar's invasion of Italy to Pompey's defeat at the Battle of Pharsalus and flight to Egypt.

It was preceded by the much longer account of Caesar's campaigns in Gaul and was followed by similar works covering the ensuing wars against the remnants of Pompey's armies in Egypt, North Africa, and Spain.

As a result of nearly ten years of conquest, Caesar had not only amassed enormous wealth but had established himself as a formidable military and political rival to Pompey.

This friendship of convenience came to an end with the death of Crassus in 53 BCE, and Pompey's marriage to Cornelia Metella, the daughter of a fierce opponent of Caesar.

Amid a fresh outbreak of political violence in Rome, Pompey was appointed sole consul in 52 and solidified his support among the Optimates in the Senate.

Caesar, meanwhile, had concluded his conquest of Gaul and, aided by the publication of his Commentarii de Bello Gallico, had become a champion of the people.

As his term as governor came to an end, Pompey and the Senate demanded that Caesar disband his army and return to Rome, and they forbade him to run for consul in absentia.

In the text, Caesar presents himself as the victim of a conspiracy occurring in Rome led by his political enemies, including Gnaeus Pompeius, Scipio, and Marcus Cicero.

Throughout the commentaries he presents his cause as a noble one to restore order and return peace to the Roman people, while showing how his actions were justified.

Caesar omits many details of the military campaigns, focusing in large part on the larger strategic situation and the reasoning behind the actions occurring.

Written as a narrative, the book begins with the expiration of Caesar's term as governor of Gaul and the party dominating the Roman Senate ordering him to return to the city to face charges of misconduct and possible execution.

Caesar and his army follow Pompeius across the Adriatic Sea to Greece after a mop up operation in Italy and in Spain.

He then proceeds to explain his reasoning for occupying Egypt with his army, using a succession crisis among the Egyptian royal family as his pretence.