That really interests me. Can you give a description
between the dates you mention. I presume Latin was still
the "lingua franca" of Rome Empire until its fall?


Latin remained the "official" language of the Western Roman Empire, but in the East Koine Greek was used. (Koine Greek is to Classical Greek as Vulgar Latin is to Classical Latin; the only difference being that Koine was written down.) Final nasals (e.g., in the singular accusative -am, -um became nasalized vowels, before disappearing altogether. The diphthong ae was probably being pronounced commonly as /ɛ/ rather than /aj/ in Caesar's time. There are a bunch of other differences. One I remember from syntax is the use of quia with the indicative mood rather than the complex system of subjunctive with a different conjunction.

I understand how the empire fragmented, but Latin just
devolved into the Romance languages? No communication
between areas of Europe caused this?


Well, I won't use the term "devolved". All the modern Romance languages are later forms of (Vulgar) Latin. The breakdown in communication exacerbated the change, but did not cause it. Languages change on their own. Having a standardized language and an orthography help to fix a language from change over a longer period than an unwritten one, but look how far many spoken forms of English are from the main national standards.

What are the Strasbourg oaths?

"The Oaths of Strasbourg were several historical documents which included mutual pledges of allegiance between Louis the German (d. 876), ruler of East Francia, and his (half-)brother Charles the Bald (d. 877), ruler of West Francia."

See the Wikipedia article (link).

For an example:

"Pro Deo amur et pro Christian poblo et nostro commun salvament, d'ist di in avant, in quant Deus savir et podir me dunat, si salvarai eo cist meon fradre Karlo et in ajudha et in cadhuna cosa, si cum om per dreit son fradre salvar dist, in o quid il me altresi fazet, et ab Ludher nul plaid numquam prindrai, qui, meon vol, cist meon fradre Karle in damno sit."

“For the love of God and for Christendom and our common salvation, from this day onwards, as God will give me the wisdom and power, I shall protect this brother of mine Charles, with aid or anything else, as one ought to protect one's brother, so that he may do the same for me, and I shall never knowingly make any covenant with Lothair that would harm this brother of mine Charles.”


Ceci n'est pas un seing.