The Gallic Wars. The Civil War. Illustrated

Caesar portrayed the invasion as being a preemptive and defensive action, but historians agree that he fought the Wars primarily to boost his political career and to pay off his debts. Still, Gaul was of significant military importance to the Romans. Native tribes in the region, both Gallic and Germanic, had attacked Rome several times. Conquering Gaul allowed Rome to secure the natural border of the river Rhine.

Caesar makes impossible claims about the number of Gauls killed (over a million), while claiming almost zero Roman casualties. Modern historians believe that Gallic forces were far smaller than the Romans claimed, and that the Romans suffered significant casualties. 

The campaign was still exceptionally brutal. Untold numbers of Gauls were killed, enslaved, or mutilated, including large numbers of civilians.