Strong nuclear interaction, has a property called color charge, holds quarks together, elementary constituents of protons and neutrons, and also the latter within the nucleus. It is absolutely the most intense force among those known so far, to the point that it is not possible at low energy to isolate and separate a single quark from a proton. Such isolation of the color charge theoretically allows long-range strong interactions only through globally neutral composite bosons by color, formed by a quark and an antiquark, in turn, linked by strong force (mesons).
However, since these are all unstable, and decaying in a short time, the strong nuclear force acts in fact only at a short distance in the nuclei. For example, the strong interaction between two nucleons can be described at low energy as the result of the exchange of Pi mesons, or pions.