Simplify the following text for a Grade 8 native English-speaking person.
Original: This expansion came to the attention of the Arsacid Great King , Artabanus IV , who ordered his vassal , the ruler of Khuzestan , to confront Ardashir .
Simplified: In conclict with Artabanus IV , who ordered his vassal , the ruler of Khuzestan , to confront Ardashir .