The revolt of the animals against Farmer Jones is Orwell's analogy with the October 1917 Bolshevik Revolution. The "Battle of the Cowshed" has been said to represent the allied invasion of Soviet Russia in 1918, and the defeat of the White Russians in the Russian Civil War. The pigs' rise to preeminence mirrors the rise of a Stalinist bureaucracy in the USSR, just as Napoleon's emergence as the farm's sole leader reflects Stalin's emergence. The pigs' appropriation of milk and apples for their own use, "the turning point of the story" as Orwell termed it in a letter to Dwight Macdonald, stands as an analogy for the crushing of the left-wing 1921 Kronstadt revolt against the Bolsheviks, and the difficult efforts of the animals to build the windmill suggest the various Five Year Plans. The puppies controlled by Napoleon parallel the nurture of the secret police in the Stalinist structure, and the pigs' treatment of the other animals on the farm recalls the internal terror faced by the populace in the 1930s. In chapter seven, when the animals confess their non-existent crimes and are killed, Orwell directly alludes to the purges, confessions and show trials of the late 1930s. These contributed to Orwell's conviction that the Bolshevik revolution had been corrupted and the Soviet system become rotten.