Complex sentence: British attention then shifted to Greece, which was under the threat of Axis invasion; while British divisions were being diverted from North Africa, the Italians were being reinforced with the German Afrika Korps under the command of General Erwin Rommel.
Split into simpler sentences: British attention then shifted to Greece, which was under the threat of Axis invasion. While British divisions were being diverted from the North African theatre, the Italians were being reinforced with the German Afrika Korps under the command of General Erwin Rommel.