Retro productive means the negative of any incident. The USA had not been involved actively in the war after the commencement of the second world war for 3 years. Japan thought that America was strong power and it would fight from the side of France one day. It decided to weaken America before it involvement in the war. So Japan bombarded at Pearl harbor of the USA. Many American soldiers were killed. Many weapons were destroyed. It was the incident of 7th Dec. 1941 AD. The very next day of this incident, America declared the war against the Axis power. The USA dropped the atom bombs called fat man on Hiroshima and Little boy on Nagasaki of Japan respectively to take revenge against Japan. About 3 lakh people died while all the people of the cities were injured or handicapped due to the Atom bombs. Defeated after this incident, Japan surrendered unconditionally. Therefore, Pearl harbor incident became retro productive to Japan.