Simplify the following text for a Grade 12 native English-speaking person.
Original: The Cholas , who re-emerged from obscurity in the 9th century by defeating the Pallavas and the Pandyas , rose to become a great power and extended their empire over the entire southern peninsula .
Simplified: The Cholas , who came back from obscurity in the ninth century by defeating the Pallavas and the Pandyas , rose to become a great power and extended their empire over the entire southern peninsula .