Simplify the following text for a Grade 9 native English-speaking person.
Original: This execution method was created by employees of Thomas Edison , and has been used only in the United States and , for a period of several decades , in the Philippines ( its first use there in 1924 under American occupation , last in 1976 ) .
Simplified: This execution method has been used only in the United States and , for several decades , in the Philippines ( its first use there in 1924 , last in 1976 ) .