They are not. A unwed mother is someone who had kid out of wedlock. A widow, is someone who's husband died, military or otherwise. You wouldn't refer to my mother as an unwed mother, since my parents were married 62 years, until father's death. When I bash unwed mothers, Incel Tears tries to make me look bad by saying that I am bashing the widows of military men who dies in action. No I am not. They are not one and the same.
