Orwell participated in the Spanish Civil War, which had two "left" sides (anarchist-syndicalist versus communist) versus the "right" (monarchist-fascist).
Within the Communist side, there were further factions (NKVD:Stalinist, POUM:other Marxist). Orwell joined POUM. As a result, he was condemned by Stalinists and had to flee back to England. He spent much of his career warning against Stalinism, from a position on what might be called the social democrat left.
I knew that the British communists (funded by Moscow) refused to give him a journalist visa for Spain, because he wouldn't promise to write whatever they told him to. His writing on Barcelona 1936 is very good, and I visited "Orwell Street"[1] there recently.
[1] It's obviously not called that, and it may be a square not a street, but I remember the street sign. :)
Within the Communist side, there were further factions (NKVD:Stalinist, POUM:other Marxist). Orwell joined POUM. As a result, he was condemned by Stalinists and had to flee back to England. He spent much of his career warning against Stalinism, from a position on what might be called the social democrat left.