Ukrainian, Belorussian and Russian

Здравствуйте, друзья!

Could anyone give me a straight answer regarding the similarities of these three languages?
From what I gather, all three belong to the Eastern Slavic subgroup, which itself comprises... only those three lingos? Kindly confirm, if you may.

Again, from what I gather and from this video https://www.youtube.com/watch?v=CUAMfg8YAU0

I should imagine the closest language to Russian would be Belorussian, not Ukrainian (because I understand more Belorussian than I do Ukrainian in that vid, and I have studied neither).

If so, then how come? How came Belorussian to evolve as an independent language, why is Ukrainian not as mutually intelligible (I hear it was heavily influenced by Polish?) with Russian and how much effort would it take for a native Russian speaker to become fluent in Belorussian? And how much do the accents differ?

Feel free to add any information that you deem important and/or interesting.

Спасибо!

Белорусский, кажется, более понятен русскоязычным, чем украинский (на слух мне так кажется). Но они оба близки русскому. Сразу без подготовки показать сложно. Но все три в одной подгруппе (восточнославянские).

This lecturer is quite well-known (Зализняк). At least I've seen him on television in discussions about languages.
http://elementy.ru/lib/431649?page_design=print

> I should imagine the closest language to Russian would be Belorussian...
Yes... But I learned this from lecture above right now.
As a russian I cannot understand fluent speech of both of them. Some words are similar, some ideas are understandable, but fluent flow of speech quickly becomes meaningless.

> How came Belorussian to evolve as an independent language
Language is very flexible construction. There are always two process accross territory: morphing into something new and melting into something similar.
You should understand that so called "old russian (slavic) language" is as much distant from modern russian, as modern russian is distant from ukranian. Moreover there were many dialects in past too.
All three modern eastern slavic languages are far from their ancient roots also. They are melted and divided from these roots by historical/political reasons.
As said in the lecture above, great role in separation of modern ukranian and belorussian from russian belongs to Grand Duchy of Lithuania. And so on.

I'm glad to see his lecture confirmed my sense of hearing.

All right, then. This would be about the same evolution as Romance languages from Latin. Dictated by historical and political context, with some room for foreign influx.

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All right, then. This would be about the same evolution as Romance languages from Latin. Dictated by historical and political context, with some room for foreign influx.

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100%.

It is fun how the same root can create absolutely different meanings in different languages.
In russian word "черствый" is "stale". However in one of the western slavic group ~"черствы" is for "fresh". Why? Common root was "strong". But in russian it was developed as "strong" -> "hard" and "hard bread" is for "stale bread". In other country "strong" was developed as "healthy" -> "young" -> "fresh". So, it is very strange for russian to read label in that country (Czech Republic) which sounds for russian something like "taintly poisoneers", which really means "fresh food".

It must be safe to say that all modern Slavic languages are derived from a common ancestor - праславянский язык (this is one of the well established theories). To use the term from the lecture in the link, this process is known as дивергенция.

The major point of interest in that lecture is development of the Russian language, i.e. the speaker suggests (largely based on his study of берестяные грамоты in Novgorod and Pskov) that the Russian language might be the result of конвергенция (the opposite process compared to дивергенция) of the two large variations, namely the north-western Novgorod and Pskov variation and central/eastern/southern variation.