What holds the protons and neutrons of a nucleus together despite the mutual repulsion between protons?

1. Protons in a nucleus repel one another through the electromagnetic force, since they carry the same charge. 2. A separate, previously unknown force holds the nucleus together despite that repulsion, called the strong nuclear force. 3. The electromagnetic force alone would push the nucleus apart, not hold it together. 4. Ordinary gravity is far too weak at this scale, and magnetism between neutrons is not the described mechanism. 5. So the strong nuclear force is correct. _Source: OpenStax Physics (CC BY 4.0), Ch 22 "The Atom", section 22.2 Nuclear Forces and Radioactivity_