Simplify the following text for a Grade 8 native English-speaking person.
Original: At a crucial moment , Confederate Maj. Gen. A.P. Hill 's division arrived from Harpers Ferry and launched a surprise counterattack , driving back Burnside and ending the battle .
Simplified: At a crucial moment , Maj. Gen. A.P. Hill 's division arrived from Harpers Ferry and launched a surprise counterattack , driving back Burnside and ending the battle .