Complex sentence: He was briefly (1942-3) the literary editor for "The Observer", until an argument with David Astor; from 1952 until his death, he was joint chief book reviewer (with Raymond Mortimer) for the London "Sunday Times".
Split into simpler sentences: He was briefly (1942-3) the literary editor for "The Observer", until a disagreement with David Astor. From 1952 until his death, he was joint chief book reviewer (with Raymond Mortimer) for the London "Sunday Times".