How did the discovery of the neutron change our understanding of the strong force?

When James Chadwick discovered the neutron in 1932, physicists gained a missing piece of the nucleus. The neutron explained why nuclei could contain more mass without adding electric charge, which helped resolve problems in nuclear structure. It also made clear that some new short-range force had to hold protons and neutrons together despite proton-proton repulsion. This eventually led to modern nuclear-force theory and, later, to quantum chromodynamics for the force between quarks. The neutron’s discovery was a turning point in both nuclear and particle physics.