Who is the enemy in the Old Man at the Bridge?

In Hemingway's short story, he observes civilians and Republican soldiers crossing over a platoon bridge as the enemy rapidly approaches the Ebro River. The short story takes place during the Spanish Civil War, and the enemy Hemingway references are the Nationalist soldiers, who are also known as the Fascists. As the civilians and soldiers are crossing the bridge over the Ebro River, the narrator notices an old man sitting alone by the side of the road. When the narrator warns him that this is not a safe place to rest, the old man tells him that he is exhausted from traveling twelve kilometers from his hometown of San Carlos. As the other civilians continue to cross the pontoon bridge, all the old man can do is lament about the loss of his animals that he once cared for. Tragically, the old man does not follow the narrator's advice and continues to sit by the road as the Fascists Army approaches. The narrator is aware that the Nationalists will surely murder the old man as they continue their advance, and mentions,

There was nothing to do about him. It was Easter Sunday and the Fascists were advancing toward the Ebro. It was a gray overcast day with a low ceiling so their planes were not up. That and the fact that cats know how to look after themselves was all the good luck that old man would ever have (Hemingway, 2).