A thermonuclear weapon, often referred to as a hydrogen bomb, is a type of nuclear weapon that uses fusion to release a massive amount of energy. This process involves combining light atomic nuclei, such as those of hydrogen, under extreme heat and pressure, resulting in a powerful explosion. Thermonuclear weapons are significantly more powerful than atomic bombs, which rely solely on fission, the splitting of heavy atomic nuclei. These weapons typically use a two-stage design, where an initial fission explosion triggers the fusion reaction. The destructive capability of thermonuclear weapons has led to global concerns about nuclear proliferation and the potential for catastrophic warfare, prompting international efforts to control their spread.