[FrenchAmerican]

My understanding is that Julius Caesar could have lost that war but there is little chance that Rome wouldn't have submitted Gaul in the end.

Current Spain and Portugal's territory required from Rome no less than 190 years of wars. Romans kept going on submitting a few tribes there every year for two centuries.

A sort of "proof" of this assertion is that Rome, in the end, conquered all territories around the Mediterranean Sea and far beyond. Of course, the course of events are by nature unpredictable but I find it reasonable tosay that the odds for a long term victory of Gaul were slim.

However, but that was much earlier, the two Punic wars against Carthage were much more existential threats to Rome.