What If Gual Unified?

Gaul would've stood a better chance against the Romans, if they were unified under one leader, but that is an ideal situation. Gaul would still struggle to unify as one nation and rivalries between tribes would've been exploited by Caesar.

The biggest problem would be the rivalry between two of the largest tribes, the Aedui and the Arverni. The two were always at each others throats, and a healthy relationship between the two would be important to the nation's stability. However, the migration of the Helvetii would prove fatal to the relationship. The Aedui would call upon Caesar to help them, and would get pulled into the Roman sphere. So when Caesar finally invades Gaul, its safe to say he could exploit the weakness between the two major factions in the nation to split the eastern Gauls from the western.

Another factor that could prove vital is the Remi. Like the Aedui, they were pro-Roman, but were actually one of the most loyal of them. According to wikipedia, they had one of the largest oppidums in Gaul, were renowned horsemen, and occupied very fertile farmlands. With these critical factors, the Remi probably would be quite powerful in the nation. With the invasion of Gaul, a possible alliance with Caesar would rob the Gauls of a major source of food and much of their mobility on the battlefield.

So, all in all, Caesar would've still rolled over the Gauls, though not as quickly.
 
Top