Simplify the following text for a Grade 7 native English-speaking person.
Original: The city-state of Athens , which became a significant cultural , political and military power during this period , was its center , where it was institutionalized as part of a festival called the Dionysia , which honored the god Dionysus .
Simplified: Theatre was part of a festival called the Dionysia , which honored the god Dionysus .