By the fourth century B.C., Iranian control of outlying areas and the internal cohesion of the empire had become tenuous. Although outlying areas like Bactriana had always been restless under Achaemenid rule, Bactrian troops nevertheless fought on the Iranian side in the decisive Battle of Gaugamela (330 B.C.). They were defeated by Alexander the Great.

Data as of July 1997
SOURCE: The Library of Congress - AFGHANISTAN - A Country Study