What are the names of the two groups in 'The Butter Battle Book'?

The two groups in “The Butter Battle Book” are the Yooks and the Zooks.

Dr. Seuss’s 1984 picture book presents the Yooks and Zooks as rival communities living on opposite sides of a long curving wall. Their dispute begins over a trivial custom: Yooks eat bread with the buttered side up, while Zooks eat it with the buttered side down.

That disagreement becomes a satire of the Cold War arms race. Each side responds to the other with increasingly destructive inventions, eventually developing the Bitsy Big-Boy Boomeroo, a small but extremely powerful bomb. The story ends without resolving which side will drop its weapon, emphasizing the danger of mutual escalation.

The names are sometimes misremembered as “Yucks and Zucks,” but the book’s spellings are Yooks and Zooks. The book was published by Random House on January 12, 1984, during the presidency of Ronald Reagan and a period of intense nuclear anxiety.

“The Butter Battle Book” was also adapted into a 1989 animated television special narrated by Charles Durning. Its unresolved ending was retained, reinforcing the original anti-war message.