George Orwell’s Animal Farm is an allegory for the Russian Revolution. Specifically, it’s a story meant to dramatize, in the form of a fable, how the political struggle that was the Russian Revolution went wrong. Every political struggle is a struggle for influence, because influence is easily translated into power.
In this case, Boxer is an influential character among the animals. He becomes the animals’ symbol for hard work and loyalty. Ironically, as he serves Napoleon even to the last ounce of his strength, he endangers his own life because Napoleon begins to fear his influence among the other animals. He doesn’t realize that Boxer is thoroughly loyal, he can only sense his power. So, he has Boxer taken away to the horse slaughterer. Afterwards, he soon finds himself struggling to explain this action when some of the animals realize what has happened.