Military campaigns of Julius Caesar
The military campaigns of Julius Caesar constituted both the Gallic War (58 BC-51 BC) and Caesar's civil war (50 BC-45BC) in 59 BC, which had been highly controversial. The Gallic War mainly took place in what is now France. In 55 and 54 BC, he invaded Britain, although he made little headway. The Gallic War ended with complete Roman victory at the Battle of Alesia. This was followed by the civil war, during which time Caesar chased his rivals to Greece, decisively defeating them there. He then went to Egypt, where he defeated the Egyptian pharaoh and put Cleopatra on the throne. He then finished off his Roman opponents in Africa and Hispania. Once his campaigns were over, he served as Roman dictator until his assassination root on March 15, 44 BC. These wars were critically important in the transition of the Roman Republic into the Roman Empire.
Gauls
The Gauls emerged around the 5th century BC as the bearers of the La Tène culture north of the Alps (spread across the lands between the Seine, Middle Rhine and upper Elbe). By the 4th century BC, they spread over much of what is now France, Belgium, Spain, Portugal, Switzerland, Southern Germany, Austria, the Czech Republic and Slovakia by virtue of controlling the trade routes along the river systems of the Rhône, Seine, Rhine, and Danube, and they quickly expanded into Northern Italy, the Balkans, Transylvania and Galatia. Gaul was never united under a single ruler or government, but the Gallic tribes were 
capable of uniting their forces in large-scale military operations. They reached the peak of their power in the early 3rd century BC.
The rising Roman Republic after the end of the First Punic War increasingly put pressure on the Gallic sphere of influence; the Battle of Telamon of 225 BC heralded a gradual decline of Gallic power over the 2nd century, until the eventual conquest of Gaul in the Gallic Wars of the 50s BC. 
After this, Gaul became a province of the Roman Empire, and the Gauls were ethnically and culturally largely assimilated into Latin (Roman settlers) majority, losing their tribal identities by the end of the 1st century AD.