This paper studies the relationship between the Coulomb force and the magnetic force in electromagnetism, and proposes the inference that the magnetic force is the concomitant force of the Coulomb force. It also proposes the hypothesis that each fundamental force has a concomitant force and extends it to gravitation, suggesting that the inertial mass is the concomitant force of the gravitational mass, and explains the Higgs mechanism. Three laws of fundamental forces and concomitant forces are summarized. A model for unifying weak interactions and strong interactions is proposed, successfully explaining why magnetic monopoles cannot exist alone and the phenomenon of quark confinement. The strengths of the strong interaction and electromagnetic interaction are explained. There is a connection between fundamental forces, their concomitant forces, and space. On the basis of the theory of concomitant forces, a model of the origin of the universe is proposed. This model provides a theoretical framework to reconcile the contradictions between quantum mechanics and general relativity.