Complex sentence: Like popular magazines and books of the 21st century, their product was aimed at as wide a public as possible, and when a book was successful it was usually followed by as many sequels as the audience would tolerate.
Split into simpler sentences: Like popular magazines and books of the 21st century, their product was aimed at as wide a public as possible. When a book was successful it was usually followed by as many sequels as the audience would tolerate.