Simplify the following text for a Grade 11 native English-speaking person.
Original: His first major debuts were at the Salzburg Festival in 1985 , followed by the London Philharmonic Orchestra in 1986 and the Orchester Musikkollegium Winterthur in 1988 . Other guest conductor appearances comprised the first five years of his career : his American debut with the Saint Louis Symphony Orchestra in 1989 , performances with the orchestras of Atlanta , Boston , New York , Chicago , plus frequent returns to the London Philharmonic .
Simplified: He appeared at the Salzburg Festival in 1985 , then conducted the London Philharmonic Orchestra in 1986 and , from 1989 he appeared a lot in the United States .