The Great Purge was real, but not how the west claims. At that time, the USSR was under threats from all sides. Nazi and polish intelligence had infiltrated the highest ranks of the soviet state. Same with reactionary groups, such as anticommunists, mensheviks and trotskists, who often collaborated with nazi and polish intelligence. First Sergei Kirov was murdered, which launched The Moscow Trials, which uncovered a vast network of spies and trotskists trying to destabilize the USSR. Seeing this, Stalin ordered NKVD head Nikolai Yezhov to begin purges to root out all these enemy elements. Keep in mind that the USSR was preparing for the eventual war with Nazi Germany. The problem was that Yezhov himself was a nazi and polish agent. He decided to begin mass purges, forced confessions and extrajudicial executions against innocent people in order to create popular anger against Stalin and destabilize the soviet government. This went on for about a year, until Stalin found out about this, removed Yezhov as head of the NKVD and appointed Lavrenti Beria, who prosecuted all those involved with this including Yezhov and stopped the purges. So yes many innocents were killed during The Great Purges but not on Stalins orders. Also many guilty people were killed to protect the USSR and socialism.

To learn more on this i recommend Grover Furr's books, he debunks many of the "stalinist crimes". "Yezhov vs Stalin" by Grover Furr is specifically about the great purges. Then you also have "Blood Lies" and "Khrushchev Lied" also by Grover Furr, which debunk more general antistalin myths, including also the great purges but in less detail. You can download all of Grover Furrs books, including the 3 i mentioned, in ebook (epub) format for free here: https://it.es1lib.org/book/12078299/732fa9