After Vasu Deva, the Kushan kingdom split in two, the
western part becoming tributary to the Sasanian monarchy. Its rulers, styled Kushanshahs, reigned over Baktria, Gandhara, and the Kabul valley. Late in the third
century, Khorasan was added to this dominion. The Kushanshahs were not perfectly
obedient vassals, but were generally friendly to Persia.
In 350 this dominion was invaded by the Epthalites or White Huns,
who were not contained until Shapur II campaigned against them,
and they then allied
themselves with Shapur against Rome.
the Kushanshah was losing Gandhara to the Kidarites, a Kushan dynasty that defeated Shapur
in 357. The Kushanshah regime ended in 400 when the Epthalites occupied the Kabul valley.
The Epthalites fell into decline in the sixth century, and in 560 the former Kushanshah dominion was conquered by an alliance
of the Sasanians and the Turks.
Epthalite territories east of the Indus gradually became Indian in character,
although coinage of crude Indo-Sasanian types continued as late as 1300.