Nuclear explosion is caused by the rapid release of energy in high-speed nuclear reaction. The driving reaction may be nuclear fission or fusion, or a cascade of the two. Although all fusion based weapons use fission devices to initiate fusion so far, pure fusion weapons are still a hypothetical device.

Mushroom like clouds are associated with nuclear explosions in the atmosphere, although mushroom like clouds can occur in large chemical explosions. Without these clouds, there could be an air blast. Nuclear explosions produce radiation and radioactive debris.

In World War II, only two nuclear weapons were deployed in combat - both against Japan. The first incident occurred on the morning of August 6, 1945, when the U.S. Army and air force dropped a uranium gun device code named "little boy" in Hiroshima, killing 70000 people, including 20000 Japanese fighters and 20000 Korean slave workers. The second occurred three days later, when the U.S. Army Air Force dropped the a-implosion device code named "fat man" in Nagasaki. It killed 39000 people, including 27778 Japanese ammunition employees, 2000 South Korean slave workers and 150 Japanese fighters. In total, these explosions killed about 119000 people. (for a complete discussion, see the atomic bombings in Hiroshima and Nagasaki.). Most governments see nuclear weapons as a "deterrent" to a large extent. The scale of the damage caused by nuclear weapons makes it impossible for people to seriously consider the use of nuclear weapons in war, thus making the concept of comprehensive war completely useless.

The main function of nuclear weapons (explosion and thermal radiation) is the same physical destruction mechanism as traditional explosives, but the energy generated by nuclear explosives is millions of times higher than that of traditional explosives, and the temperature reached is within tens of megakelvin. Nuclear weapons are very different from conventional weapons in that they can release huge explosive energy and can produce various effects, such as high temperature and nuclear radiation.

Like conventional explosives, the devastating impact of an explosion does not stop after the initial explosion. The radiation cloud propagates from the epicenter of the explosion, even after the heat wave stops, it still affects the life form.

Any nuclear explosion (or nuclear war) will have a wide range of long-term disastrous effects. Radiation pollution will lead to gene mutation and cancer in many generations.