1. I have not said that analytic language cannot appear in a close knit society, only that the vast majority of the time polysinthetic and highly synthetic languages occur only in close knit societies, and that languages used in civilized socities have a strong tendency to be or become more analytic.
I present for your consideration... FRENCH!*
2. See above.
3. Besides the americas and the caucasus, polysynthetic languages only occur in a language family in extreme northwestern siberia, oceania (australia, new zealand, polynesia etc) and one language family in northeastern india (the Munda languages). All of these, including that part of india are close knit, village/band based socities.
I present for your consideration... meh, this is getting boring. Also, when was the jump from synthetic to polysynthetic justified in your posts? If we include just synthetic languages in our count, we get languages like Russian, Finnish, Turkish, Hungarian, Polish, Japanese, ... included in our count.
4. This has simply not been the case, however. Besides, i'm talking in a grammatical sense, not really the length of the words themselves or the amount of compound words.
Yeah, I agree this point was kind of weak, but I think once you 1) present a decent metric for synthesis, and 2) present a decent statistical model, you'll find that global amount of synthesis probably is rather independent from degree of civilization.
6. Relatively they were advanced and large socities, but they were still close knit in the sense that most people only lived in one village their entire lives.
Russia. Hungary. Finland. France.
* sure, French is written as though it is just a bit synthetic, on less of an order really than Russian. However, if French were not a written language today, and field linguists came in and started taking notes, they'd agree it's polysynthetic, and they'd make up an orthography that reflects this. Keep this in mind as well - there's no 100% clear way of determining whether a language is polysynthetic or isolating, and oftentimes, all what we go by is the tradition entrenched in the orthography.