Atomic Bombs are no ordinary weapons; they are very powerful packing a big punch. The big explosion from the bombs are produced from the result of sudden release of energy. When a neutron strikes a nucleus of an atom of the isotopes uranium-235 of plutonium-235, it causes that nucleus to split. In the process of splitting a great amount of energy is released. The series of rapidly multiplying fissions culminates in a chain reaction in which all fissionable material is consumed, in the process of what is known as an Atomic Bomb.
Japan suddenly bombed America in a surprise attack specifically, Pearl Harbor. Outraged, Congress declared a war on the country on Japan. This caused World War Two to explode, an all-out war of anger and competition