Complex sentence: Most men that followed Du Died in the Burmese jungle of tropical disease and starvation or were killed by the Axis forces, while Sun's army retreated in an orderly fashion into India.
Split into simpler sentences: Most men that followed Du Died in the Burmese jungle of tropical disease and starvation or were killed by the Axis forces. On the other hand, Sun's army retreated in an orderly fashion into India.