Complex sentence: Meanwhile, Auchinleck reorganised Allied forces and strengthened them to two corps, XXX and XIII, which formed the British Eighth Army, which was placed under the command of Alan Cunningham.
Split into simpler sentences: Meanwhile, Auchinleck reorganised Allied forces and strengthened them to two corps, XXX and XIII, which formed the British Eighth Army. The Eighth Army was placed under the command of Alan Cunningham.