Complex sentence: It has been run since 2003, sanctioned by the National Auto Sport Association it is the successor to the Timex 12 Hours of Thunderhill event run between 1998 and 2002.
Split into simpler sentences: It has been run since 2003, sanctioned by the National Auto Sport Association. It is the successor to the Timex 12 Hours of Thunderhill event run between 1998 and 2002.