What was the historical setting of the world in 1946, the copyright date of Animal Farm? What effect did this have on Orwell's work?
In 1946, World War II had just ended (Orwell actually finished the book during the war but it was not published until after) and the Cold War was in its very early stages. I think that this affected Orwell's work by making him even more disillusioned with the Soviet Union and its system (he was something of a leftist but didn't like the Soviet Union).
By this time, the Soviet Union had existed for almost 30 years and it would have been clear to most people that it had not really done what it had promised to do. Specifically, it had not brought prosperity or equality to its people. Instead, it had brought hardships and terror both through its domestic policies (Stalin's purges, etc) and through Stalin's flirtations with Hitler before the war.
I think that this history inspired Orwell to write this critique of the leaders of the Russian Revolution. It is also something of a critique of all those who think that they can bring a perfect society into existence (which would have seemed pretty unlikely to a person who had just seen WWII happen).
1946 marked the end of World War II, but Communist Russia began asserting itself and began to dominate international politics. This resulted in the beginning of the Cold War and Europe itself being divided into two camps - one capitalist like West Germany, and the other communist like East Germany.
Orwell, like many others, was totally disillusioned by the consequences of the communist revolution in Russia in 1917. Instead of an open - In March 1946 Churchill coined the phrase "the iron curtain - egalitarian society, by 1946 the USSR had become a brutal dictatorship with no respect for human rights.
His disillusionment is expressed bitterly in the concluding lines of "Animal Farm" :
No question, now, what had happened to the faces of the pigs. The creatures outside looked from pig to man, and from man to pig, and from pig to man again; but already it was impossible to say which was which.