In Another Country

Is it important to know that the narrator of the story an American soldier? 

It is important to understand that the narrator in "In Another Country" is an American soldier because one of the themes of the story is isolation. The fact that the narrator is an American in a foreign country isolates him. Most of his companions are not Americans, plus he has been wounded and is, therefore, isolated from the battlefield. Even the setting of the hospital is isolated because is it "beyond a bridge" separated from the main part of the town.