Simplify the following text for a Grade 8 native English-speaking person.
Original: It was signed on May 15 , 1955 , in Vienna at the Schloss Belvedere among the Allied occupying powers ( France , the United Kingdom , the United States , and the Soviet Union ) and the Austrian government .
Simplified: It was signed on May 15 , 1955 at Vienna between the Allied powers from World War II and the Austrian government .