Jamieson, Fausset and Brown on Numbers 22:6

6. Come ... curse me this people--Among the heathen an opinion prevailed that prayers for evil or curses would be heard by the unseen powers as well as prayers for good, when offered by a prophet or priest and accompanied by the use of certain rites. Many examples are found in the histories of the Greeks and Romans of whole armies being devoted to destruction, and they occur among the natives of India and other heathen countries still. In the Burmese war, magicians were employed to curse the British troops.