The Chambord castle

The borders of modern France are roughly the same as those of ancient Gaul, which was inhabited by Celtic Gauls. Gaul was conquered for Rome by Julius Caesar in the 1st century BC, and the Gauls eventually adopted Roman speech (Latin, which evolved into the French language) and Roman culture. Christianity took root in the 2nd century and 3rd century AD, and became so firmly established by the fourth and fifth centuries that St. Jerome wrote that Gaul was the only region “free from heresy”. In the Middle Ages, the French would adopt this as a justification for calling themselves “the Most-Christian Kingdom of France.”
In the 4th century AD, Gaul's eastern frontier along the Rhine was overrun by Germanic tribes, principally the Franks, from whom the ancient name of "Francie" was derived. The modern name "France" derives from the name of the feudal domain of the Capetian Kings of France around Paris. Existence as a separate entity began with the Treaty of Verdun (843), with the division of Charlemagne's Carolingian empire into East Francia, Middle Francia and Western Francia. Western Francia approximated the area occupied by modern France.
The Carolingians ruled France until 987, when Hugh Capet, Duke of France and Count of Paris, was crowned King of France. His descendants, the Capetian, Valois and Bourbon dynasties progressively unified the country through a series of wars and dynastic inheritance. The monarchy reached its height during the 17th century and the reign of Louis XIV. At this time France possessed the largest population in Europe (see Demographics of France) and had tremendous influence over European politics, economy, and culture. Towards the end of this era, France played a major role in the American Revolution by providing capital and some military assets to the anti-British rebels.