It may fairly be argued that the eight years from 58 BC to 51 BC were the most decisive in the history of France, and indeed of Western civilization. In the course of those eight years, Julius Caesar conquered most of Gaul, a region corresponding roughly to modern France, plus much of present-day Belgium and Switzerland. In the process, he transformed what had been essentially a Mediterranean empire and civilization into one that extended into the heart of continental Western Europe.
Roman rule over Gaul lasted five centuries after Caesar, but its effects were permanent. We need only consider the fact that though France bears the the name of a Germanic tribe, the Franks, who conquered Roman Gaul, the French language is derived neither from the Franks nor the Celtic Gauls, but from Latin. The French may speak of "our ancestors, the Gauls," but their civilization is Roman, and in the centuries after Rome fell they transmitted that civilization to lands where no legion ever marched.
Had there been no Roman conquest of Gaul, the subsequent history of Europe would surely have been unimagineably different. There could have been no Western Empire as such; the Roman Empire as a whole would have resembled an enlarged Byzantine Empire, with its wealth and vitality centered in the East, and Western Europe would have developed along entirely different lines, perhaps developing as a pagan, Celtic society, perhaps even eventually being incorporated in the Islamic world. Such alternatives are the sheerest speculation; we can only say with some confidence that France and the West as we know them would have been impossible.
The remainder of this discussion will be devoted to the strategic and tactical dimensions of Caesar's conquest of Gaul, with the central theme being the ways in which Caesar's methods employed established Roman methods in new ways to solve problems that were new to Roman experience. The exceptional nature of C...