Factbox - North Korea says successfully conducts first H-bomb test

By Idrees Ali and Jonathan Landay WASHINGTON (Reuters) - North Korea said on Wednesday it had successfully tested a miniaturised hydrogen bomb, leading to questions about what a hydrogen bomb is, why it is seen as a threat, and how the test could be detected. ATOMIC BOMBS--The first nuclear weapons, developed during World War II, atomic bombs, or fission weapons, use a process by which neutrons collide with an atom’s nucleus and release energy with explosive force. U.S. aircraft dropped at