Veche as a form of government had roots in tribal assembiles in Eastern Europe, it's true that Novgorod and Pskov are more prominent examples, but it's not limited to them.

Saying, however, that a switch from "democratic" Kiev to "authoritarian" Moscow led to demise of these older forms of government is incorrect. Direct democracies like veche were practiced all over Europe, and most of them were gradually replaced by more authoritarian and centralized forms of government.

Sorry I can't think of an English-language sources at the moment.

It's tough to call any state from that period "liberal", but I would agree that Kievan Rus was at least somewhat less authoritarian than post-Mongol Muscovy. I would say, though, that calling it "democratic" would be going much too far. Here's a series of selections from the Cambridge History of Russia, volume 1:

"Essentially, the vast ‘land of Rus” was a family unit, with all the affinities and tensions germane to that term, and there were no effective ritual or legal mechanisms making for a generally accepted succession. Once the family ‘patriarch’ died, these uncertainties could only be resolved by a virtual free-for-all between the more or less eligible sons of Vladimir. The coming of Christianity fostered economic well-being, fuller settlement of the Black Earth region and cultural advance, while a kind of ‘cult of personality’ now invested Vladimir, accentuating the aura of princely blood. Over the centuries there would scarcely ever be a question of persons who were not his descendants seizing thrones for themselves in Rus’." (p. 72)

"Political legitimacy in Rus’ resided in the dynasty. The ruling family managed to create an ideological framework for its own pre-eminence which was maintained without serious challenge for over half a millennium." (p.74)

"The princes of Rus’ were warlords, heading a military elite." (p. 81)

It is true that in Kievan Rus authority was less centralized than in later Muscovy, but this is due more to practicalities than to any kind of democratic ideology:

"Rus’ external political relations were thus as unitary or as diffuse as were Rus’ domestic politics. During the rare periods of comparatively unitary domestic authority–under Vladimir Sviatoslavich,for example, or under Iaroslav once he became ‘sole ruler’ after 1036–it may be possible to identify a comparatively coherent foreign policy. Otherwise the separate princes’ dealings with their non-Rus’ neighbours were largely – and increasingly – autonomous." (p. 93)

Finally, we know very little about Kievan Rus' history beyond high politics:

"Beyond the prince, his retinue and parts of the city, evidence for social or administrative structures becomes very sparse indeed. In other words, we know very little about the vast majority of the population...visions of early Rus’ range from a cluster of ‘city states’ sustained partly by slave labour and partly by the surplus produce of a free peasantry, to a ‘feudal’ economy based on the growth of aristocratic manorial estates and a largely dependent peasantry. In addition, the overall picture may have to accommodate wide regional differences. These are, of course, major issues, but the visible pieces of the jigsaw allow too many plausible but conflicting reconstructions to justify full confidence in any of them." (p. 87-88)

Anyway, the point of all these quotations is that we have no reason to believe Kievan Rus was democratic in anything close to the modern sense of the word. It was ruled by princes, who were "chosen" through dynastic struggles, usually including warfare, and neither the general population nor any class other than the ruling military elite had any real say in politics. It was certainly less authoritarian than Russia as unified by Muscovy, but that's more a reflection of a more general trend in Europe at the time, as /u/haimgelf said.

I own a book called Reinterpreting Russian History: Readings, 860-1860's, and there is an essay early on which discusses democracy in Kievan Rus. It is written by Ia. Froianov and A. Iu. Dvornichenko, and they state that Novgorodian democracy was not an oddity in the Kievan political landscape. They go as far to state,

"The election of princes was the result of a single process, common to all Rus' in the eleventh and twelfth centuries, of formation of city-states, the supreme organ of which was the popular assembly, within whose competence, among other things, came the filling of princely thrones."

Froianov and Dvornichenko then say that the plunder of Kiev in 1169 by Suzdal resulted in the political power of Kiev's community being broken, as an unelected prince was placed on the throne by the conquerors. If you are interested in pre-Soviet Russian history, I would highly recommend finding the book at your library.

Thanks guys for answering my question! : )