Simplify the following text for a Grade 8 native English-speaking person.
Original: Westphalia is a region in Germany , centred on the cities of Arnsberg , Bielefeld , Bochum , Detmold , Dortmund , Gelsenkirchen , Hagen , Minden and MÃ 1\/4 nster and included in the state of North Rhine-Westphalia .
Simplified: Westphalia is a region in Germany . The cities of Arnsberg , Bielefeld , Bochum , Detmold , Dortmund , Gelsenkirchen , Hagen , Minden and MÃ 1\/4 nster are in its center .