RIA Novosti explains:
The Cossacks are a military estate that existed in Russia before the revolution of 1917 and served in border areas. Russia’s Cossacks numbered more than 4.4 million in 1916. There were 11 Cossack military formations in the country in the early 20th century. The Cossacks were abolished as an estate in 1920. In 1936, several Cossack cavalry larger units were activated and later fought Nazis in the Great Patriotic War of 1941-45.
Until the Russian Revolution, there were some 4 million Cossacks. Abolished by Lenin in 1920, Stalin revived the Cossacks in 1936, and Cossack Units fought the Germans in World War II. After the war, the Cossacks were again disbanded. (Thanks to Siberian Light for the tip.)
What caught my eye here is the word “abolished.” Not only did Bolsheviks abolish the Cossack estate, which was natural as the old, antiquated estate system had to be put to rest. They literally abolished — killed that is — a large number of Cossacks (with help from the poorer Red Cossacks); many others were resettled. This policy was known as “De-Cossackization” (raskazachivanie); it peaked during the Civil War and the Collectivization.
“Cossacks” once described communities of those who had moved out or escaped from Muscovy and Poland-Lithuania to live a life of robbing and farming in the huge steppe area in-between the sedentary agricultural Ruthenia and its various neighbors, including the unpleasant steppe nomads. Russians slowly but surely colonized the steppe and closed in on their troublesome neighbors in the South and the South-East, leaving less space for the Cossacks’ highwaymanship.
The Russian Cossacks then stroke a bargain with Moscow, promising to perform military service, as frontier guards in particular, in return for a degree of self-government. Turns out I have written about them before. But keeping in mind the Civil War of 1918–1922 and the Collectivization, I doubt if many of the inhabitants of Russia’s traditionally Cossack areas are descended from pre-1917 Cossacks. Are we going to see a new Cossack estate emerge when Russian rebels and misfits stream down south and all the way to the Far East, Russian borders in need of protection more than ever since 1700?