How Does Fusion Produce Energy?

What exactly are the mechanisms holding atoms together and why does bringing them together create energy? ------------------------------------------------- Relevant Papers: On the Mechanism of Nucleon-Nucleon Attraction by Pion Exchange - https://doi.org/10.4236/jmp.2018.98090 A reappraisal of the mechanism of pion exchange and its implications for the teaching of particle physics - https://hst-archive.web.cern.ch/archiv/HST2002/feynman/Pion%20exchange.pdf Origin and properties of strong inter-nucleon interactions - https://arxiv.org/pdf/1308.0103.pdf FUSION POWER BY MAGNETIC CONFINEMENT PROGRAM PLAN VOL I - https://fire.pppl.gov/us_fusion_plan_1976.pdf Kinetic Energy to Temperatue - https://colab.research.google.com/drive/1OfwMiHkUZzi_M8BbygHnJ4zlVu3h5pnP?usp=sharing