One often encounters a narrative within older works on the Germanic peoples that goes something like this: late BC Germanic societies were largely democratic, featured elective kingship, and the kingship in question was religious or at least ritualistic in nature. However, the subsequent centuries militarized Germanic society and caused a rise in warlords - men who were powerful because they had been successful in war and could gather warriors to themselves. Is there any truth to any of this?
English speaking scholars would say no. German scholars, you'll get conflicting answers.
The book you should read to see this argument in action is probably H. Wolfram, History of the Goths (a 1988 translation and revision of his 1980 German text). He draws heavily on R. Wenskus, Stammesbildung..., which argues that barbarian 'tribes' were based around elites who preserved ancient traditions, surrounded by followers who did not themselves share a common blood / heritage, but were united in a tribe (or ethnicity) via the shared traditions to which they ascribed. This is what the 'ethnogenesis' or Vienna school grew out of, and History of the Goths is a great example of the arguments they contributed to what became a miserably divisive debate that still fractures German archaeology.
W. Goffart published Barbarian Narrators in 1988, in which he argued that we need to read late antique literary sources as works of literature rather than objective collections of ancient oral traditions (which is how Wolfram, drawing on a strand of German scholarship that goes back to the 18th century, reads texts like Jordanes). If sources are read as Goffart suggests, the pseudo-philological foundations on which the notion of ancient Germanic kingship were built crumble, and this is precisely what Goffart and his students began to argue in what became a systematic attempt to disembowel traditional Germanic prehistory. E.g., you can't take Tacitus at face value, and you can't use him to reconstruct ancient German social systems: you have to read him as a product of the 2nd century.
Goffart and his students (the Toronto school) went on to pick fights with Wolfram and his, which resulted in a lot of acrimonious publications, the most vitriolic of which is probably the edited volume Gillett, On Barbarian Identity 2002. You should read this volume, as it gives a good overview of all the critiques of the view of Germanic society you're asking about. It also breaks down into accusations of neo-Nazi sympathizing nationalist scholarship, and ends with a response by one of the scholars who was called out as a Nazi sympathizer... it's academia at its ugliest and most dramatic. But: well worth a look.
In the following 15 years or so, things have settled down a bit, though German scholars are still intensely divided on whether to continue traditional interpretations of the archaeology, or to adopt newer post-modern / post-processual readings of literary and archaeological sources. You definitely still see people writing about the Germanic Gefogschaft, sacred kings, and ancient warlike traditions. But among English speaking scholars, that makes you look a bit like a neo-Nazi, or at the very least someone who's 20 years out of touch with the field - which doesn't mean people don't still make this argument, a lot.
Christ, I'm writing a conference paper on exactly this.
Much depends upon how far back you choose to trace "Germanic" society. I know for the Visigoths, it depends entirely on how much stock you place in a continuity that traverses the Danubian crossing of 376 through to their formal settlement in Toulouse in 418.
If you believe that there is continuity from the pre-Danubian period all the way through Toledo (i.e. Wolfram's pals), then regardless of Roman influence, there is a Germanic "core" that survived all the way to the Visigothic Spanish phase.
Goffart's people feel otherwise.
The key splitting point in the debate is basically your trust in the 6th century writer Jordanes and the "accuracy" of the chain of information going to him, from Germanic "oral" stories, through to Cassiodorus, through to him. If you believe that Jordanes' writings reflect the actuality of the Visigothic past, then you follow Wolfram. However if you're more skeptical, because you treat, as /u/alriclofgar said, the source as literature, then you're left with very little in the way of sources contemporary to the Visigothic crossing that can tell you about how their society actually functioned.
I myself am taking the latter position. Frankly Kulikowski's 2006 book "Rome's Gothic Wars" explains it far better than me, but essentially, he points out that if we don't teleologically backfill our narratives from Jordanes, then a contemporary reading of the sources suggests there was nothing for the Visigoths to transform. Namely, the Visigoths as we know them in the post-Danubian period are creations of their interactions with the Romans, and there is no relationship with a "Germanic society" which existed before.
The debate is still alive and well. I mean Peter Heather takes a more measured approach. Certainly the idea of integrated nations migrating is useful to modern politics, but when it comes to the burden of evidence, the fact that our sources say little to nothing about how kingship functions, allows both sides to say nearly whatever they want about its structure.
And that's why The Dark Ages™ is so great. You get to write historical fiction and pass it off as history (but then again, isn't it all a literary construction? etc. etc. etc. etc. etc.)