Complex sentence: Calvera spares the gunmen's lives, believing that they have learned that the simple farmers are not worth defending; he also fears reprisals from gunfighter friends of theirs from north of the border.
Split into simpler sentences: Calvera spares the gunmen's lives, believing that they have learned that the simple farmers are not worth defending. He also fears reprisals from gunfighter friends of theirs from north of the border.