Good explanation, but it kind of buried the lede. The answer is way down at the bottom: > Fission releases the energy of the electromagnetic force when positiv

Good explanation, but it kind of buried the lede. The answer is way down at the bottom: > Fission releases the energy of the electromagnetic force when positively charged parts of the nucleus fly away from one another. Fusion releases the energy of the strong force (much stronger at short distances than the EM force) when the small pieces are captured and held into one nucleus.