Simplify the following text for a Grade 8 native English-speaking person.
Original: Chief Opechancanough led a coordinated series of surprise attacks of the Powhatan Confederacy that killed 347 people , a quarter of the English population of Jamestown .
Simplified: The number killed , 347 , was almost one-third of the English population of Jamestown . They were killed by a number of surprise attacks by the Powhatan Confederacy ( a Native American tribe ) , who were ruled by Chief Opechancanough .