Complex sentence: The Roswell High books served as inspiration for the television series Roswell (1999-2002), also known as Roswell High in some countries, which in turn spawned a number of spin-off books of its own.
Split into simpler sentences: The Roswell High books served as inspiration for the television series Roswell (1999-2002), also known as Roswell High in some countries. Roswell spawned a number of spin-off books of its own.