The more I read about early Medieval history (600AD-1100AD), the more confused I become about European cultural traditions.

Take the above mentioned neighbors, Germany and France for example. Or, to describe them slightly differently, the Kingdom of the Eastern Franks and the Kingdom of the Western Franks. In other words, each of the two countries is descended from Charlemagne's realm (along with Northern Italy, of course). But there are such radical differences between the two countries: language, interpretation of Salic law, the form that feudalism took, the list goes on and on.

And as far as I know, there were no major migrations into one or the other country since they were united. What gives? If nothing else, I'd really like to nail down the language issues.. why do the French speak a Romantic language (with minor German influences) while the Germans speak a Teutonic langague (with minor Latin influences).

Also, is modern French a combination of Langue d'Oc and Langue d'Oil or did one win out over the other... Why?