As a fiction writer, I wouldn't say Lugones is a brilliant writer, but there are some things I think he does well. One of them is write about fatalism and love, which seem often to be connected in his works. His Cuentos Fatales is intriguing in starting off like a sequel to Fuerzas Estrañas before transforming into an exploration of those entwined concepts. In a way, it's almost not surprising that Lugones killed himself in part over an unrequited infatuation.
"Juramiento" is the story of a royalist officer captured by a montonero raid on a fort. The montoneros want to execute him but feel he must first be allowed to heal from the injuries he received in the fighting. They take him to the home of a young widow who supports the patriotic (i.e. Independence) cause. While the officer heals, he and the widow, though sworn enemies, fall in love. For me, that part of the story, though cliché, worked pretty well, due for Lugones' talent at conjuring up romantic love as a kind of surrender to destiny.
However, the end of the story was awful or perhaps just dated. The officer decides to join the independence movement, mostly out of that same sense of destiny. He is accepted by the montonera, and he and the widow ride out and give short speeches about patriotism. The widow is decked out in blue and white, which happen to be the colors of the Argentine flag, so the patriotic symbolism hits incredible heights of obviousness.
It's possible I'd like this story more if I didn't know that Lugones would go on to become something of a fascist. It's easy to see in the combination of fatalism and patriotism as precursors to fascism. Or maybe it's that the patriotism in the book strikes me as a bit simplistic. My skeptical mind suspects that the gauchos of Salta might have been fighting for some less abstract than just the homeland, and that playing up their patriotism renders them dull saints to Argentine nationhood.