Snowball studies the battles of Julius Caesar to learn battle techniques and prepare for the fight against the humans. He is a wise pig and after the animals run Farmer Jones and his men off the farm, he knows they will eventually fight back. The humans are upset that the now-liberated animals are trying to spread the word to animals on other farms to rebel against human control. The human masters forbid the singing of the Animalism fight song "Beasts of England" on their farms and live in fear that more revolts will occur. They would like very much to win back control of Animal Farm to show the other animals that such rebellions are doomed to failure.
But because of Snowball, the animals are prepared when the attack comes. Snowball has them organized by animal type—birds, pigs, horses, etc.—and they eventually surround the humans from the rear and defend against the attack in ways that grow more dangerous. They defeat the humans after Boxer kills a "stable lad."
Snowball learned his battle strategy from a book on Julius Caesar's military battles.