Why is the anime split into Dragon Ball and Z, but the manga isn't?

Open a Japanese collection at any point in the run and the title never changes: from 1984 to 1995 the manga is Dragon Ball, one continuous series of 519 chapters. The Z exists only because of television. The anime ran as Dragon Ball from 1986 to 1989, through the Piccolo arc; for the era of the adult Goku, Toei relaunched the show in 1989, and the anime staff wanted a freshened title for the new run.

They asked Toriyama for one. His explanation, given in the 2003 TV Anime Guide, is the most honest title story in the business: "Z is the last letter of the alphabet. I really already wanted to end the comic, so I gave the title a 'Z' with the meaning of 'That's all, folks.'" The show then ran until 1996 anyway. The popular story that a handwritten 2 was misread as a Z is a fan myth; the Z was a deliberate, slightly exhausted joke.

The split hardened in the West for a different reason: Viz Media divided the English manga into Dragon Ball (volumes 1 to 16) and Dragon Ball Z (volumes 17 to 42) to match the television branding American readers knew. A TV marketing line, drawn in 1989, became a border in the bookshelf that Japan never had.