Because cluster bombs release many small bomblets over a wide area, they pose risks to civilians both during attacks and afterwards. Unexploded bomblets can kill or maim civilians and/or unintended targets long after a conflict has ended, and are costly to locate and remove.
Cluster munitions are prohibited for those nations that ratify the Convention on Cluster Munitions, adopted in Dublin, Ireland in May 2008. The Convention entered into force and became binding international law upon ratifying states on 1 August 2010, six months after being ratified by 30 states. As of 1 April 2018, a total of 120 states have joined the Convention, as 103 States parties and 17 Signatories.
The first cluster bomb used operationally was the German SD-2 or Sprengbombe Dickwandig 2 kg, commonly referred to as the Butterfly Bomb. It was used in World War II to attack both civilian and military targets. The technology was developed independently by the United States, Russia and Italy (see Thermos Bomb). The US used the 20-lb M41 fragmentation bomb wired together in clusters of 6 or 25 with highly sensitive or proximity fuzes.
Artillery shells that employ similar principles have existed for decades. They are typically referred to as ICM (Improved Conventional Munitions) shells. The US military slang terms for them are "firecracker" or "popcorn" shells, for the many small explosions they cause in the target area.