A hydrogen bomb, also known as a thermonuclear bomb, is a type of nuclear weapon that uses fusion to release a massive amount of energy. Unlike atomic bombs, which rely on fission (splitting heavy atomic nuclei), hydrogen bombs combine light atomic nuclei, such as those of hydrogen, to form heavier nuclei, releasing energy in the process. This fusion reaction occurs at extremely high temperatures and pressures, typically achieved by detonating a fission bomb first. The destructive power of a hydrogen bomb is significantly greater than that of traditional atomic bombs. For example, the bomb dropped on Hiroshima in 1945 was far less powerful than modern hydrogen bombs, which can yield explosions equivalent to millions of tons of TNT. The development of hydrogen bombs has raised concerns about global security and the potential for catastrophic warfare.