the nuclear force

Protons carry positive charge, so a nucleus packed with them should blow itself apart by electrostatic repulsion. It does not, because a far stronger attraction acts between nucleons at short range and overwhelms the Coulomb push. That short-range glue is the nuclear force, the thing that makes nuclei exist at all. It is powerful but has an extremely short reach: essentially zero beyond a couple of femtometres.

The nuclear force has three signature features. It is strongly attractive over about 1 to 2 fm but turns sharply repulsive (a hard core) at very short distances, which is why nuclear matter does not collapse and has nearly constant density. It is roughly charge-independent, treating proton-proton, neutron-neutron and proton-neutron pairs almost alike (isospin symmetry). And it is spin-dependent and non-central, including a tensor component, which is essential to even bind the deuteron. Historically, Yukawa modelled it as arising from the exchange of massive mesons (principally pions), and the finite pion mass explains the finite range: heavier exchanged particle, shorter reach.

The deep point is that the nuclear force is not fundamental. It is the residual, leftover effect of the truly fundamental strong interaction, quantum chromodynamics, which binds quarks into protons and neutrons via gluon exchange. The force between whole nucleons is a spillover of the color force, analogous to the way the van der Waals force between neutral atoms is a residue of the underlying electromagnetic force between their charges. Pion-exchange is an effective, low-energy description of that residue, not the bedrock theory.