What forces cause protons to repel each other?

Protons repel each other due to the electromagnetic force, which is one of the four fundamental forces of nature. Since protons are positively charged particles, they experience a repulsive force when they come close to one another, as like charges repel. This electromagnetic repulsion is significant, especially within atomic nuclei, where protons are held together by the much stronger nuclear force, which overcomes this repulsion at very short distances.