Battle of Alesia
Caesar engaged in the Gallic Wars (58–50 BC), which led to his conquest of Gaul beyond Gallia Narbonensis. When the Helvetii, a federation of tribes from what is now Switzerland, planned a migration to the Atlantic coast through Gaul, Caesar went to Geneva and forbade the Helvetii to move into Gaul. While he went to Gallia Cisalpina to collect three other legions, the Helvetii attacked the territories of the Aedui, Ambarri, and Allobroges, three Gallic tribes, which called for Caesar’s help. Caesar and his Gallic allies defeated the Helvetii. The Gallic tribes then asked for Caesar to intervene against an invasion by the Suebi, a Germanic tribe. Caesar defeated the Suebi. In 57 BC he intervened in intra-Gallic conflicts and marched on the Belgae of northern Gaul. From then on he conquered the Gallic peoples one by one. His successes in Gaul brought Caesar political prestige in Rome and great wealth through the spoils of wars and the sale of war captives as slaves.
Democratic elements of Roman Republic
After Sulla's death, republican rule was more or less restored under Pompey the Great. Despite his popularity, he was faced with two astute political opponents: the immensely wealthy Crassus and Julius Caesar. Rather than coming to blows, the three men reached a political accommodation now known as the First Triumvirate. Caesar was awarded governor of two Gallic provinces (what is now France). He embarked on a campaign of conquest, the Gallic War, which resulted in a huge accession of new territory and vast wealth not to mention an extremely battle hardened army after eight years of fighting the Gauls. Crassus, jealous of Caesar's successes, embarked on a campaign in Parthia, where he was defeated and killed in the Battle of Carrhae. In 50 BC Caesar was recalled to Rome to disband his legions and was put on trial for his war crimes. Caesar, not able to accept this insult after his fantastic conquest, crossed the Rubicon with his loyal Roman legions in 49 BC. Caesar was considered an enemy and traitor of Rome, and he was now matched against the Senate, led by Pompey the Great. This led to a violent Civil War between Caesar and the Republic. The senators and Pompey were no match for Caesar and his veteran legions and this culminated in the Battle of Pharsalus, where Caesar, although outnumbered, destroyed Pompey's legions. Pompey, who had fled to Egypt, was murdered and beheaded.