Simplify the following text for a Grade 3 native English-speaking person.
Original: The interaction of long time Postville residents with newcomers was the subject of a book about the town , Postville : A Clash of Cultures in Heartland America ( ISBN 0-15-100652-0 ) , written by Stephen Bloom , a professor at the University of Iowa .
Simplified: Postville is a city of Iowa in the United States .