Simplify the following text for a Grade 11 native English-speaking person.
Original: Initial production was based only in Japan , but since 1994 the American market has been served by vehicles assembled at the former Diamond-Star Motors ( DSM ) facility in Normal , Illinois .
Simplified: At first is was only made in Japan , but since 1994 the American market has been supplied by vehicles assembled at the former Diamond-Star Motors ( DSM ) facility in Normal , Illinois .