The ICBM, or Intercontinental Ballistic Missile, is the game-ending superpower of Military nations in the Civilization Stage, unlocked when 6 cities are captured. It costs 60,000 Sporebucks to use, but the cost decreases with the amount of cities left to capture.
When used, it launches a number of missiles out of the city hall, corresponding to the number of cities left to capture. When the missiles hit the enemy cities, they instantly destroy the city hall, along with all vehicles and spice derricks. When all cities are destroyed, the player moves on to the Space Stage. Using this grants you the Conclusion Achievement.
Background sounds include whistling and a 'YEEEHAWWW', the latter of which is a reference to the closing sequence of the movie Dr. Strangelove with Major Kong "riding the bomb". Many buildings are turned into nuclear waste piles upon contact.