Complex sentence: From 1969 to 1971, he worked at the CBS News London bureau, and from 1971 to 1977, was based in the London and Saigon bureaus, where he worked as a Vietnam War correspondent.
Split into simpler sentences: From 1969 to 1971, he worked at the CBS News London bureau. From 1971 to 1977, he was based in the London and Saigon bureaus, where he worked as a Vietnam War correspondent.