Simplify the following text for a Grade 13 native English-speaking person.
Original: Six days after the detonation over Nagasaki , on August 15 , Japan announced its surrender to the Allied Powers , signing the Instrument of Surrender on September 2 , officially ending the Pacific War and therefore World War II .
Simplified: Six days after the explosion over Nagasaki , on August 15 , Japan announced its surrender to the Allied Powers , signing the surrender paper on September 2 , officially ending the Pacific War and World War II .