ICBM (or Intercontinental Ballistic Missile) is a generic term for rocket systems developed for the long range delivery of nuclear warheads. Made famous during the Cold War, missile systems (as developed by the USA and Soviet Union) were engineered quickly, driving the Space Race between the two superpowers. The term Mutually Assured Destruction (MAD) was coined during this era, as tensions were so great, if one nation launched a nuclear attack, the other would immediately respond, thus assuring destruction of both countries. The nuclear standoff lasted for decades and due to current-day nuclear proliferation, smaller nations are able to develop their own ICBM systems.
Missile defence systems have been developed in the hope of destroying ICBMs in flight before their deadly payloads can be delivered.