The French language was originally called "Latin". When Julius Caesar invaded, he was so succesful at coming, seeing and conquering (bar a small village in Armorica), that everyone there started to speak Latin. The French then started to get so sloppy with their Latin, (presumably because they were sick to death of having to work out the declension of "mensa" every time they wanted to call someone a "thick-head"), as well as allowing Gaulish words to sneak into their vocabulary, that they started to speak a dialect of Latin called "French". The reason most Francophiles get annoyed when French is referred to as "A degenerate form of Latin" is therefore because it is true.
Not everyone in France actually spoke French. There were a significant number of non-Latin descended languages in France, and the South of France spoke a similar language refered to as the langue d'oc, or Occitan. In fact it was mostly those in Paris who spoke French as we know it, but when the French Revolution came a law was passed forcing everyone in France to suffer the language of the Parisians. Ever since then, bodies such as the "Acadamie Francaise" have ensured that French does not get infected by English words (such as television), and to retain the "purity" of the French language.
The relationship between French and the other native languages of France is an interesting one. Up until the early part of the twentieth century the official response of the French government to anybody trying to speak another native French language, such as Breton or Occitan (which is now officially referred to as a dialect), was to charge them with treason, and signs were erected in fishing villages in Brittany warning "No spitting or speaking Breton". Some people may find this attitude hard to reconcile with French complaints of the dominance of the English language, but it must be realised that the reason French governments have done this is because they are certain that their language is superior.