Why is napoleons a pig

All of this is not, of course, merely a study in one pig’s power play. Napoleon does not make sense unless you realize that he is a double for Joseph Stalin, who served as the General Secretary of the Communist Party from 1922 until his death more than 30 years later. Like Napoleon, Stalin was a master at pulling strings behind the scenes. He grew a secret police force, the NKVD (later the KGB), which behaved a bit like Napoleon’s dogs, ultimately proving its by assassinating Leo Trotsky, Snowball’s double and one of Stalin’s chief rivals.

The links between Joseph Staline and Napoleon the pig are:
They are both greedy and they are both really powerful and wealthy.
As Joseph Staline has got his own secret police force called KGB, Napoleon the pig has got his own little army made of poppies.