Purges - People who opposed the system were executed or pushed out using the Secret Police (Napoleon's dogs)
Show trials were used to quash any dissention (Confessions of animals conspiring with Snowball)
Idea of 'New Man'/'New Woman' - the ideal Communist who worked for a record breaking number of hours (Boxer's "I will work harder" maxim)
Lenin's cult of personality - his body was put on display after he died (Display of Old Major's skull)
Hitler forged an alliance with Stalin in 1939 but found himself fighting against Stalin's army in 1941. Hitler's forces were defeated in the Battle of Stalingrad, although the city itself sustained huge damages (Hitler represented by Frederick)
The Kronstadt rebellion was a major, unsuccessful rebellion against the Bolshevik party in 1921.(Hen's attempts at uprising by breaking their newly hatched eggs)
In the Tehran Conference of 1943, Churchill, Roosevelt and Stalin came together to try to forge lasting peace after war (a peace that Orwell mocks by having Napoleon and Pilkington flatter each other and then betray their duplicitous natures by cheating in the card game)

Animal Farm Background