Gauls
In 58 BC Julius Caesar launched the Gallic Wars and had conquered the whole of Gaul by 51 BC. He noted that the Gauls (Celtae) were one of the three primary peoples in the area, along with the Aquitanians and the Belgae. Caesar's motivation for the invasion seems to have been his need for gold to pay off his debts and for a successful military expedition to boost his political career. The people of Gaul could provide him with both. So much gold was looted from Gaul that after the war the price of gold fell by as much as 20%. While they were militarily just as brave as the Romans, the internal division between the Gallic tribes guaranteed an easy victory for Caesar, and Vercingetorix's attempt to unite the Gauls against Roman invasion came too late. After the annexation of Gaul a mixed Gallo-Roman culture began to emerge.
Campaign history of the Roman military
During a term as praetor in Iberia, Pompey's contemporary Julius Caesar of the Roman Julii clan defeated the Calaici and Lusitani in battle. Following a consular term, he was then appointed to a five-year term as Proconsular Governor of Transalpine Gaul (current southern France) and Illyria (the coast of Dalmatia). Not content with an idle governorship, Caesar strove to find reason to invade Gaul, which would give him the dramatic military success he sought. To this end he stirred up popular nightmares of the first sack of Rome by the Gauls and the more recent spectre of the Cimbri and Teutones. When the Helvetii and Tigurini tribes began to migrate on a route that would take them near (not into) the Roman province of Transalpine Gaul, Caesar had the barely sufficient excuse he needed for his Gallic Wars, fought between 58 BC and 49 BC. After slaughtering the Helvetii tribe, Caesar prosecuted a "long, bitter and costly" campaign against other tribes across the breadth of Gaul, many of whom had fought alongside Rome against their common enemy the Helvetii, and annexed their territory to that of Rome. Although "fierce and able" the Gauls were handicapped by internal disunity and fell in a series of battles over the course of a decade.