Why did Stalin Launch the Great Terror, 1936-38?

In 1932 things looked very good for Stalin; the First Five Year Plan was complete, the peasants had been collectivised and Stalin was the 'boss' and firmly in control. However, there was still a little opposition in the Communist Party and a Party member called Ryutin circulated criticism of Stalin and how he ran the Party among the Central Committee arguing for his removal as General Secretary. Of course, Stalin was furious that someone of so little importance had the audacity to say circulate such things, so he demanded that Ryutin should be executed and it was put to the vote. …