Simplify the following text for a Grade 7 native English-speaking person.
Original: Under the terms of the Greater Berlin Act of 1920 , KÃ penick became a borough of Berlin , with an area of , making it Berlin 's largest borough .
Simplified: KÃ penick was an independent town until 1920 . It then became a borough of Berlin , with an area of , making it Berlin 's largest borough .