The strong force is what keeps nuclei together. It is described by a theory called quantum chromodynamics (QCD), which described the forces between fermions called quarks that make up the hadrons. The...The strong force is what keeps nuclei together. It is described by a theory called quantum chromodynamics (QCD), which described the forces between fermions called quarks that make up the hadrons. These forces are mediated by spin-1 bosons called gluons.