Soldier specifically refers to the Army. Marines are called Marines. Naval personnel are called sailors. Air Force personnel were called "airmen" but I assume they've probably come up with something gender-neutral by now. No idea what Space Force settled on but "spacemen" would be hilarious. Warfighter is meant to be a blanket term for all uniformed personnel of the armed forces that doesn't only include the Army.

At least that is the US terminology. I can't speak for other countries.