"Farewell to Cheyenne" from the original score to Once Upon a Time in the West by Ennio Morricone
I couldn't find the background chords to this theme so decided to work it out.
Am D Am
Am D Am D
G B Em
Em D
Am D Am
Am D Am D
G B Em
Em D
Pretty sure this is right though there is some moving bass notes below the chords, particularly on the Em.
See the link: http://www.filmmusicnotes.com/
ennio-morricones-score-for-once-upon-a-time-in-the-west-part-2-of-3-cheyennes-theme/
for additional info if you need