nuclear fusion is the process by which multiple nuclei join together to form a heavier nucleus.
Nuclear fusion of light elements releases the energy that causes stars to shine and hydrogen bombs to explode.
Nuclear fusion of heavy elements (absorbing energy) occurs in the extremely high-energy conditions of supernova explosions.
Nuclear fusion in stars and supernovae is the primary process by which new natural elements are created.
It is this reaction that is harnessed in fusion power.
It takes considerable energy to force nuclei to fuse, even those of the lightest element, hydrogen.