88790
The postage stamps and postal history of Azerbaijan describes the history of postage stamp s and postal system s in Azerbaijan , which closely follows the political history of Azerbaijan , from its incorporation to the Russian Empire in 1806 , to its briefly obtained independence in 1918 , which it lost to the Soviet Union in 1920 and re-acquired it in 1991 after the fall of the Soviet Union .
 Azerbaijan, Azerbaijan, Azerbaijan, Russian Empire, 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:
 Azerbaijan, Azerbaijan, Azerbaijan, Russian Empire, Soviet Union