What is the physical requirement for nuclear fusion that necessitates the plasma state?

Answer

It requires atomic nuclei to approach closely enough to overcome their natural electromagnetic repulsion.

In the plasma state, the stripped electrons allow the positively charged nuclei to approach much closer under intense pressure, enabling quantum tunneling and fusion reactions to overcome electrostatic repulsion.

What is the physical requirement for nuclear fusion that necessitates the plasma state?
astronomycompositionstarmatterplasma