the following is from https://www.reddit.com/r/communism101/comments/316tey/forced_deportation_under_stalin/

As is the case with many anti-Stalin claims, the originator of the “forced deportation” distortion is none other than Nikita Khruschev:

Comrades, let us reach for some other facts. The Soviet Union is justly considered as a model of a multinational state because we have in practice assured the equality and friendship of all nations which live in our great Fatherland. All the more monstrous are the acts whose initiator was Stalin…the mass deportations from their native places of whole nations…without any exception…not dictated by any military considerations…

If you know your Soviet history, you should also know that many of the things Khruschev says in his “Secret Speech” are pure bullshit. This allegation is no different. I don’t reject the fact that there were mass deportations of certain ethnic groups, but contrary to Khruschev’s supposition, these mass deportations were actually driven by military considerations. After all, WWII was going on in the background, particularly in the rear of the Red Army.

So you want non-bourgeois sources, huh? Keep in mind that many bourgeois historians have done good work on the USSR, not every Sovietologist is Robert Conquest or Richard Pipes. But I do have a copy of Furr’s book, so I’ll borrow from that a bit. The first large-scale deportation of a specific ethnic group came in 1937, when about 175,000 Koreans living on the Chinese border were forcefully relocated to Kazakhstan and Uzbekistan because they were allegedly spying for the Japanese. Now, I know what you’re thinking: it is simply improbable that almost 175,000 people would all be spying for a foreign enemy. Furr responds by saying that if “only the guilty” were punished, the nation as a whole would split, and its survival would be threatened. Young men were usually the demographic involved in conspiracies, and if only they were deported, you could probably make an educated guess what would happen to the group altogether. So instead, tactics of mass deportation were used to keep the groups intact. Were the accusations of espionage veracious? Well, here’s what Stalin said to the famous defector, Genrikh Samoilovich Lyushkov:

It is necessary to clean up the army and its rear in the most determined manner from hostile spy and pro-Japanese elements…the Far East is not Soviet, there the Japanese rule…Stalin resumed the conversation by saying it was necessary in cleansing the rear to terrorize the Korean district and the frontier so as to prevent any Japanese espionage work.

According to Lyushkov, Stalin ordered the deportations “from the standpoint of counter-intelligence”. He sincerely believed that the Koreans in the Far East had spies for the Japanese in their midst. Hiroaki Kuromiya covered the topic extensively in his The Voices of the Dead: Stalin’s Great Terror in the 1930s. He writes that the Soviet-Japanese border areas “had been tense for some time”. One Soviet report dated December 25, 1934 describes two Chinese spies sent by the Japanese being detained on their side of the border. On December 28, a Soviet border guard was shot at by four unknown men from the “Manchu” side. And on the very next day, a Japanese plane invaded Soviet air territory near Grodekovsky (гродековский). In 1936, according to Japanese estimates, there were 203 border disputes with the Soviet Union. Still, despite all of this, Kuromiya contends that it isn’t clear whether any of the ethnic Chinese and Koreans deported were actually spies. History suggests that Japan very well may have been extensively using espionage tactics, as they used them in both the Russo-Japanese War and the Siberian Civil War. Knowledge of the prevalence of black ops near the border areas combined with Stalin’s conversation with Lyushkov should lead honest people to the conclusion that the mass deportations were not based on racism or hatred for Japanese culture, but fear.

There is no “alleged” here. Whether someone wants to justify it, or contextualize it or not, the deportations are well documented and no secret. You can find a lot of sources via Marxists.org though expect spin both from the texts and the works they are citing. Neither can adequately cover the whole experience of an ethnic group.

In Blackshirts and Red’s Parenti makes a point of saying that these internal deportations are crimes of state and wrong, but that the numbers are often inflated. The mistreatment of the Ingush and Chechens went back a decade prior complicating things.

https://www.marxists.org/history/erol/periodicals/marxist-leninist-research-bureau/mlrb-07.pdf https://www.marxists.org/history/etol/newspape/isj2/2000/isj2-086/ferguson.htm https://www.marxists.org/archive/bland/1993/07/enforced-resettlements.pdf

The 1/4th death toll I think is correct, but that’s not for the Mountain SSR deportations alone, that’s for the batch of them post WW2.