Simplify the following text for a Grade 8 native English-speaking person.
Original: The cars were Sprint Cup Series and Camping World West Series cars and the field was by invitation for the two races , run after the 1996 and 1997 seasons .
Simplified: The cars were from the Sprint Cup Series ( then called Winston Cup ) and Camping World West Series ( then called Winston West ) . The field was by invitation for the two races , and the field included several Japanese and Australian drivers .