Complex sentence: The Sussex Spaniel was one of the first ten breeds admitted into the stud book by the American Kennel Club in 1884, but lost what little popularity it had achieved in the 1940s.
Split into simpler sentences: The Sussex Spaniel was one of the first ten breeds admitted into the stud book by the American Kennel Club in 1884. The breed lost what little popularity it had in the 1940s.