Simplify the following text for a Grade 7 native English-speaking person.
Original: In his speeches in the late 1920s , Nazi leader Adolf Hitler complained bitterly about the presence of Jewish conductors at the Berlin opera , and mentioned Walter a number of times , adding to Walter 's name the phrase , `` alias Schlesinger . ''
Simplified: In the late 1920s , the Nazi leader Adolf Hitler often complained that conductors at the Berlin opera were Jews .