Complex sentence: The Imperial Japanese Army also engaged in the execution and harsh treatment of Allied military personnel and POWs and biological experiments were conducted by Unit 731 on civilians and prisoners of war; this included the use of biological and chemical weapons authorized by Emperor Shōwa himself.
Split into simpler sentences: The Imperial Japanese Army also engaged in the execution and harsh treatment of Allied military personnel and POWs. Biological experiments were conducted by Unit 731 on prisoners of war as well as civilians; this included the use of biological and chemical weapons authorized by Emperor Shōwa himself.