How can nuclear fusion be uncontrolled? as there are no trigger like new nitrogens in fission?

Nuclear fusion starts at, or triggered by, high temperature, about 100 million K. At such temperature, hydrogen nuclei (i.e. protons) will have sufficient energy to overcome the electrostatic repulsion between the nuclei. Should the energy released by fusion reaction be able to maintain the temperature, the reaction would be sustained.

(Note: how come nitrogen be involved in fission reaction ???)