When did Erin Hunter start to write?

Erin Hunter, the pseudonym for a team of authors including Kate Cary, Cherith Baldry, and Tui T. Sutherland, began writing in the early 2000s. The first book in the popular "Warriors" series, "Into the Wild," was published in 2003. The series quickly gained a dedicated following, leading to numerous sequels and spin-offs within the "Warriors" universe.