 Tolkien suggested in his notes that the dwarves that turned to wickedness most likely came from the far eastern mansions (and perhaps some of the nearer ones) which came under the Shadow of Morgoth and turned to evil.It is unclear if these refer to Dwarves beyond the Iron Hills (the most eastern known stronghold of the Dwarves).Because Dwarves are not evil by nature, few ever served the Enemy of their own free will (though rumours of Men suggest the total was greater).