Complex sentence: He saw action in the First World War, where he was seriously wounded, and during the Second World War he commanded the Eighth Army from August 1942 in the Western Desert until the final Allied victory in Tunisia.
Split into simpler sentences: He saw action in the First World War, where he was seriously wounded. During the Second World War he commanded the Eighth Army from August 1942 in the Western Desert until the final Allied victory in Tunisia.