Germanic people from various tribes (or only those from Northern Germany?) of the time (pre-Roman/Christianization) migrated north into the areas of Scandinavia. With this migration they bought with them their 'pagan' beliefs and language. At some point these Germanic people became what we know as 'Norse' and were later referred to as 'Vikings', their language (from the Northern Germany area?) evolved over time into "Old Norse": therefore names for Gods changed, such as the Germanic 'Donar'/'Donner' became 'Thor'. The majority of Germany is then Christianized and Germanic paganism ceases over time. However, the Norse religion lives on as a sub-set of Germanic paganism, until Scandinavia is also Christianized later.

What throws me off is that the majority of historical texts that describe these gods, the German people, the Vikings, etc, are from a time of either having been converted to Christianity (such as the Sagas from Iceland) or from an outsider's perspective (such as Tacitus and his Germania work), or are from archaeological findings that can only tell us so much.

So I guess my question is: Did the Norse and their religion/beliefs originate from Germany (specifically Northern Germany)? And from my writing above (from what I've read so far), what I have said is correct?