How did Napoleon distort history?
In the story that Orwell wrote, Napoleon represents the real life Joseph Stalin of the Soviet Union. Napoleon certainly distorts the truth in Animal Farm, particularly when he gets rid of Snowball under false pretenses.
When Napoleon relates to the other animals why Snowball left Animal Farm, he does distort history, in a way, to suit his purposes. He sets Snowball up to be a traitor so that he can blame him for all the suffering and turmoil that the farm experiences once Napoleon takes full charge.
The animals all believed in Snowball's ideas and witnessed his heroism at the Battle of Cowshed. When Napoleon tells the story of the Battle of Cowshed, he distorts history by telling the animals that Snowball was not a hero as they believed, but a traitor who was a spy working with Farmer Jones against them. He has been working with the humans all along, he tells the other animals, a lie.
In fact, Napoleon is the one who has been working with the humans for his own purposes, to get rich to have alcohol and enjoy a life of pleasure while the other animals do all the hard work on the farm, with little food and rest.
He does this to suit his needs to manipulate and control everything. He also has the propagandist, Squealer, who informs the other animals of Snowball's behavior giving it an official tone. Napoleon uses Squealer to shape the truth into whatever he wants it to be.
"Snowball is proclaimed a traitor against Animal Farm, in league with the humans from the beginning. Even now, Squealer assures the animals, Snowball is preparing to lead another human attack on the farm."