27604
Russia was plunged into the Russian Revolution , which threw down the Tsarist monarchy and replaced it with the communist Soviet Union .
 Russia, Tsarist monarchy, Soviet Union
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Russia, Tsarist monarchy, Soviet Union