Simplify the following text for a Grade 7 native English-speaking person.
Original: Elsewhere , he became the Australian Opera 's Music Director in 1970 , conducting the first performance in the Sydney Opera House in 1973 ( the Australian premiere of War and Peace by Sergei Prokofiev ) .
Simplified: From 1970 he was Music Director of Australian Opera . He conducted the first performance in the new Sydney Opera House in 1973 conducting Prokofievâ s opera War and Peace .