Complex sentence: The Chindits were trained to operate deep behind Japanese lines, their operations were marked by prolonged marches through extremely difficult terrain by underfed troops weakened by diseases such as malaria and dysentery.
Split into simpler sentences: The Chindits were trained to operate deep behind Japanese lines. Their operations were marked by prolonged marches through extremely difficult terrain by underfed troops weakened by diseases such as malaria and dysentery.