What were the most important things Julius caeser accomplished?

Julius Caeser had a critical role in the events that led to the demise of the Roman Republic and rise of the Roman Empire.

Julius Caesar rose to power as part of the First Triumvirate, an alliance between Caesar, Pompey and Crassus. The First Triumvirate shared responsibility for ruling Rome between the three of them. Caesar's focus was on the territory of Gaul, now occupied by modern France. Serving the role of consul and later governor, Caesar brought all of Gaul under Roman control, making it a Roman province and defending the territory against the Helvetians and Germans. During this time Caesar also invaded parts of England and put down a major rebellion by Gallic chieftains.

After the death of Crassus, Julius Caesar went to war with Pompey. Caesar was remarkably successful, quickly driving Pompey from Italy. Following his early victory, Caesar successfully invaded Spain, which had been loyal to Pompey. He eventually defeated Pompey in 48 B. C. at the Battle of Pharsalus in Greece. He went on to win several more battles in the Mediterranean after defeating Pompey.

Caesar was preparing to invade the Parthian Empire when he was famously assassinated in 44 B. C. by political rivals who stabbed him 23 times.