'1984' should be read in conjunction with 'Animal Farm' and 'Homage to Catalonia'. In 'Animal Farm', Snowball, the opponent of Napoleon is quite obviously Trotsky. The pun in Napoleon's name is that Stalin was viewed by Trotsky as a 'Buonapartist'. 
 'Homage to Catalonia' is an account of Orwell's adventures in Spain, including his time in the P.O.U.M. militia. One of the leaders of P.O.U.M. was Andres Nin, who was one of Trotsky's secretaries. Orwell was radicalised by Spain, and also made into a bitter opponent of both Fascism and Stalinism.