The Gallic Wars were a series of military campaigns waged by the Roman proconsul Julius Caesar against numerous Gallic tribes between 58 BC and 50 BC. They culminated in the decisive Battle of Alesia in 52 BC, in which a complete Roman victory resulted in the expansion of the Roman Republic over the whole of Gaul (mainly present-day France and Belgium). While militarily just as strong as the Romans, the Gallic tribes' internal divisions helped ease victory for Caesar; Vercingetorix's attempt to unite the Gauls against Roman invasion came too late. Although Caesar portrayed the invasion as being a preemptive and defensive action, most historians agree he fought the wars primarily to boost his political career and to pay off his massive debts. Still, Gaul was of significant military importance to the Romans, as native tribes, both indigenous to Gaul and farther to the north, had attacked them several times. Conquering Gaul allowed Rome to secure the natural border of the Rhine river.