The Remi (a Belgic tribe) witnessed Rome’s recent conquest of southern Gaul. The attuned tribe created a plan of opportunity for political independence and economic gain from their chaotic and disorganized neighboring tribes.
A natural frontier was also lacking between Suessiones and Remi. The Remi admitted to Caesar that there had been a virtual state of union between them, and the easiest interpretation is that certain prominent Remi decided to gain independence from the Suessiones by joining Caesar. Source: Wightman, Edith M. (1985). Gallia Belgica. University of California
Although of the same race, the Remi distrusted their Gallic neighbors because of their Germanic origins. According to the Remi, years before the conquest, the Atrebates, Menapii, and other local tribes had crossed the Rhine, displaced the indigenous Belgae, and settled. This centuries-old conquest by the Germani remained a point of dissention within the Remi. The Remi were subsequently opposed to new Gallic-Barbarian alliances.
Sensing discord in the region, Caesar accepted the Remi’s proactive intelligence and logistical support in exchange for protection from the chaos that seemed to be ensuing in the Gallic regions. Because of the Remi, Caesar deftly obtained a political victory that enhanced his military capability.
Source: Caesar, Julius. The Battle for Gaul. Translated by Anne and Peter Wiseman. Boston: David R , Publisher, Inc., 1980.