A nuclear weapon is a powerful explosive device that derives its destructive force from nuclear reactions, either fission or fusion. These weapons can release immense energy, resulting in devastating blasts, heat, and radiation. They are primarily designed for military use and can cause widespread destruction and loss of life. Nuclear weapons were first developed during World War II, with the United States creating the first atomic bombs, known as Little Boy and Fat Man. Since then, several countries have developed their own nuclear arsenals, leading to ongoing discussions about nuclear disarmament and global security.