What fundamental physical action characterizes nuclear fusion occurring in the stellar core?

Atomic nuclei collide with enough energy to overcome electrical repulsion and merge

Nuclear fusion, often termed stellar nucleosynthesis in this context, is defined by the specific interaction occurring at the nuclear level under extreme conditions. Atomic nuclei naturally possess positive charges, meaning they repel each other due to the electromagnetic force. For fusion to occur, the nuclei must be moving at incredibly high velocities—imparted by extreme core temperatures—so that their kinetic energy allows them to collide with enough force to overcome this natural electrical repulsion. Upon overcoming this barrier, the strong nuclear force takes over, binding the colliding nuclei together to form a single, heavier nucleus, releasing massive amounts of energy in the process.