American Triangle is a magnificent piece of work in my judgement. Harrowing, dramatic and stately are words that come to my mind as I listen to this song. The lyrics paint a picture of stark images contrasted against John Ford like western scenery. Elton's singing is passionate. And it's made all the more poignant by the fact that it's based on the sad but true-life murder of Matthew Shepard.
You don't find many pop songs set in minor keys but this is one and it serves the song well. American Triangle is in C-minor, the relative minor of Eb and as you know, one of Elton's favorite keys. The intro is a descending diatonic progression that most musicians should recognize. The slash chords facilitate the melodic bass line movement.