Izba

Izba (изба) is a traditional Russian countryside house, a kind of log house. It was the house of the conventional Russian farmstead ...


Source Wikipedia article: http://en.wikipedia.org/wiki/Izba
 

Strel'tsy

Military Unit (musketeers). Czar Peter had them hanged. See Wikipedia article:

http://en.wikipedia.org/wiki/Streltsy

source: http://en.wikipedia.org/wiki/Streltsy

Greatcoat

Dates back to the 15th century, I mention Strel'tsy a couple of lines down in the poem; it is what they would have worn.  As for the beards: Peter the Great demand that the Boyars (muscovite aristocracy) cut their beards and westernize.

land pirates - Cossacks

Here I am reffering to the Cossacks; they were granted autonomy by Muscovy (Russia's old gevernment). Though it's not very definitive and more info is available, you can read the Wikipedia article:

http://en.wikipedia.org/wiki/Cossacks

Caucus

1. Appointment of or allocation of votes for presidential candidates within a party (United States).


2. An area in the Eastern European Republic of Armenia.

Think about both definitions.
Source: http://en.wiktionary.org/wiki/caucus

Don

a European river in southwestern Russia; flows into the Sea of Azov


source:  http://wordnet.princeton.edu/perl/webwn?s=don

Blackgaurd

According to Marriam Websters Online dictionary: [I am using the 2nd def.]

Pronunciation: \ˈbla-gərd, -ˌgärd; ˈblak-ˌgärd\
Function: noun
Date: 1535

1obsolete : the kitchen servants of a household

2 a: a rude or unscrupulous person b: a person who uses foul or abusive language