Complex sentence: From 1981 to 1985 he was principal guest conductor of the Los Angeles Philharmonic Orchestra, and from 1988 to 1995 he was principal conductor of the London Symphony Orchestra, becoming principal guest conductor thereafter.
Split into simpler sentences: From 1981 to 1985 he was principal guest conductor of the Los Angeles Philharmonic Orchestra. From 1988 to 1995 he was principal conductor of the London Symphony Orchestra, becoming principal guest conductor thereafter.