Complex sentence: There were two possible targets for the Allies to attack: either into Sicily and then on to Italy, or into Greece and the Balkans to trap the German forces there between the British and American forces and the Soviets.
Split into simpler sentences: There were two possible targets for the Allies to attack. The second option was into Greece and the Balkans, to trap the German forces present between the British and American invaders and the Soviets.