Why do we find Crimean Tatars in Kazakhstan and so forth? As a short answer, it's because Stalin seen them as a threat.

Crimean Tatars and Chechens&Ingush were basically genocided via death marches (as it's recognised by various nations and bodies, like later recognised by the EP) Karachay and Balkars, Kalmyks and such also faced mass deportations of their entire nations. First ones has been replaced by various national groups but mainly by Russians, and rest also faced similar fates in their countries being destroyed until Krushchev let them to return back even though they weren't rehabilitated. It was more of an effort to neutralise countries and regions that were under Russian control since the times Russian Empire seized them in the 19th century more or less. That's not something that new for Russia either, like they did a similar thing in Circassia in the means of death marches and mass deportation of the whole nation, and replaced native Circassians with various groups but mainly Russians and then little-Russians. The official reasons for the Stalin's mass deportations in those areas were collaborating with Nazis. Collaboration was partially true for Crimean Tatars while they collaborated less than Ukranians and Russians of course, and had many also fought under and/or alongside the Soviet Army. For Chechen and Ingush, it wasn't even partially true since Nazis never made to there and no Chechen or Ingush fought for Nazis while rebels clearly informed iii. Reich that they'll also fight with them if they try to invade their land and act like masters. The real reason was of course getting rid of anything that would seem like a future threat to Russia, and colonise the lands with 'reliable' and 'loyal' populations starting with ethnic Russians.

Stalin also mass deported other various groups that he perceived as a threat to USSR/Soviet Russia. Like Meshketian Turks and Karapapaks, Volga Germans, Crimean Greeks, Italians of Crimea, Kuban Greeks are the ones comes to my mind when it comes to ones deported as the whole groups. Most of them allowed to return back after the death of Stalin, and with Krushchev denouncing his policies. Although again, no real rehabilitation efforts or anything.

When it comes to Korean mass deportation; it was the first ethnic cleansing Stalin did, and compared to ones he did during the WWII, it was milder and not a death march, nor accompanied mass starvation and massacres. Although it was tragic anyway. The official reason was to prevent Japanese infiltration. Well, at least we can say it was about the security of Russia.

Baltics have another story, but not that much of a different one. Part of their populations were deported in order to neutralise them and subjugate them. It started with deportation of officers, members of student organisations, former politicians and so on which already constituted a significant part of their population, and arguably one that really mattered for the nation. After Soviets took the region back from the iii. Reich, there was another deportation wave. Of course, it also followed with Estonia and Latvia having 'reliable' settlers, most of whom were ethnic Russians.