Joseph Stalin - The Gravedigger

'[Michal] Reiman’s argument is that, far from being a logical consequence of socialism, the methods Stalin employed were “a complete break with the meaning and essence of the social doctrine of socialism”. But this break did not occur because of the programme of 1917 or even because of some thought out ideology on Stalin’s part.  Rather, Reiman argues, in 1927 the USSR faced an immense economic and political crisis, to which Stalin and his supporters responded “pragmatically”.
It was out of these pragmatic responses that the Stalinist system grew – and in turn shaped the mentality of those who ruled over it, Stalin included, so that “Stalin in 1929” was very different to “Stalin in 1926” in “the general nature of his politics” and the “type of practical solutions he proposed”...'
  From Chris Harman's review of The Birth of Stalinism, the USSR on the Eve of the “Second Revolution” by Michal Reiman

Edited to add: Ian Birchall on Stalin's River of Blood