Nuclear forces are said to hold protons and neutrons together. what is it about the composition of the nucleus that requires the concept of nuclear forces?

The nuclear force is the force that binds all the particles found inside the nucleus. The nucleus is the very dense part of an atom. It occupies very little space, but the majority of the element's mass resides in the nucleus. Because of the little space, there is a great attractive force between neutrons and protons. That is why nuclear reactions are associated with very high energy reactions because you need to break the nuclear force in order to create a new element.