What is the difference between a soldier and a combatant?

Every soldier is a combatant. But not all combatants are soldiers.

Soldiers belong to A Nation
Combatants belong to an ideology

I think most of the British fatalities were sailors who died when their ships were torpedoed. Perhaps this was the difference they were highlighting.

In the fighting sports "combatants" is frequently used. Like boxers, wrestlers or MMA fighters.

None though are soldiers, yet soldiers do go into combat.

id argue that a soldier has legitimate basis from a recognized governmental body or state and an implied level of professionalism whereas combatants is more blanket term for anyone who took up arms.

e.g. in the revolutionary war in the us, the British fielded soldiers (and mercenary soldiers, but still soldiers) - they largely met on battlefields in groups expecting to meet other large groups. Americans were largely farmers who happened to have hunting rifles and would do things like use cover, climb into trees and target fire specifically at command personnel, all of which was considered cowardly, unprofessional, and out of the range of "rules" of the day.

so in some ways America invented guerilla warfare and haven't managed to win against it since.

If a civilian picks up a gun and starts shooting at Argentinians, they are a combatant. That does not make them a soldier, soldiers are people who are actually integrated into one army's command structure and are on their payroll.

It's just a grammatical artifact. Simply put, it avoids using the same word twice in one sentence. I obsess over this all the time when I write. There's no difference at all, just two words for the same thing. Similes, Synonyms... something like that, just makes if more readable.

I think it's like comparing different countries or states.

WA - Beautiful 1 day & perfect the next.

Vic - Rain & Overcast most days & bush fires whenever the sun is out