General Information
The Soviet Union (also known as the USSR) is a socialist country that is playable from December 30th, 1922 to December 25th, 1991 (Fall of the Soviet Union). After the Second World War the 
USSR set up many communist satellite governments in Eastern Europe. January 1st, 1947 is bookmarked in the game as the beginning of the Cold War. This was a time period where the 
USA and the USSR were the two greatest powers standing after the war, both ascending to the title of a "superpower". The USSR went on to have many outstanding achievements, including being the first in many space related achievements, although not represented in game. The USSR eventually collapsed in 1991, due to a failing economy, political liberalization (that allowed the many dissidents to finally express their views and seek the creation of independence movements), nationalist sentiments in annexed countries (specifically the annexed Baltic states) and an expensive relationship with 
Cuba.
See also: 
Russia, 
Ukraine, 
Belarus, 
Estonia, 
Latvia, 
Lithuania, 
Finland, 
Poland, 
United States, 
France, 
Japan, 
Manchukuo, 
Iran, 
Germany, 
Spain, 
Mongolia, 
Tannu Tuva, 
China, Cuba, 
Yugoslavia, 
East Germany, 
Romania, 
Hungary, 
Moldova, 
Czechoslovakia, 
Bulgaria, 
Albania
Soviet Union Strategy
WWII
Cold War
(Historic) Vassal Strategy
This is a more historical game option, where saving Monarch points and maintaining a large military is crucial. The player would have to go to the console commands and vassalize all Warsaw Pact members, along with Mongolia, as was the Soviet system during the cold war. The player will want to start building all possible buildings, along with creating more army (The USSR starts out with around half of its manpower limit). This strategy leaves 4 diplomatic relations slots open, and often the player will find himself wanting alliances with 
India (If the game is started after the release of India by 
Britain) and 
Saudi Arabia. Great Britain will accept an alliance under the right conditions, though they will be provoked if you choose to attack Iran or 
Afghanistan. If the player wants to avoid long alliance chains, a day one war with any nation will do (you have the Imperialism Casus Belli), though historic options will be Iran, Finland, or Afghanistan ( China will go after Afghanistan if enough time passes). Annexation of a vassal is possible sometime in the 1960s, Poland or Romania are the usual first targets.
During this time, wars in Europe will ensue. 
West Germany will often go to war with smaller neighbors looking for provinces, dragging the rest of Western Europe. Colonies will declare independence. If the player chooses not to ally Great Britain, usually one or more British colonies will be looking for your support for independence. Now will also be a good time to start fabrication of claims in China. America will be a constant thorn in your side, usually sabotaging your reputation (this can be fixed by improving relations over time). Naval power will become more important to the player soon, so building a navy will be important as well. If China is not allied with the USA, this would be a good time for a war. India usually will join and of course all your vassals will as well. You can take Manchuria or the Gobi Desert region in this war, either is not much more valuable than its counterpart. Your aggressive expansion will be high, so keeping quiet is a good idea (you shouldn't declare another war until your diplomatic reputation penalty goes away from annexing a vassal).
Decisions
End of Soviet Union
Requirements:
- Is
Soviet Union - Government Form is not:
- Communist Dictatorship
- Socialist Republic
- Is not a subject nation
- At Peace
Upon Enactment:
- Country changes to Russia
- Gain20 Prestige
- Gain Russian Traditions & Ambitions
Form Soviet Union
Requirements:
- Is Russia
- Soviet Union does not exist
- Government Form is:
- Communist Dictatorship or
- Socialist Republic
- Is not a subject nation
- At Peace
Upon Enactment:
- Country changes to Soviet Union
- Gain 20 Prestige
- Gain Soviet Traditions & Ambitions
Soviet Ideas and Traditions
Traditions:
- National Manpower Modifier +50%
Ideas:
- Collectivization of Land: +10% National Tax Modifier
- State Atheism: +2 Yearly Prestige & -2 Tolerance of Heretics, Heathens, and the True Faith
- Proletariat Rule: -10% Stability Cost Modifier
- Hammer and Sickle: +10% Production Efficiency
- Red Army: +50% Land Force Limit Modifier & -20% Infantry Cost
- Gulag System: -1 National Unrest
- Revolution: -25% Unjustified Demands
Ambitions:
- -20% Infantry Cost
- +0.5 Yearly Army Traditions