Bektuzun and Fa'iq now form an alliance in order to stop Mahmud of Ghazni, who wants all of Khurasan for himself.
Fearing that Mansur will betray them to Mahmud, the two depose and then blind him in February 999, then appoint Mansur's younger brother 'Abd al-Malik II as amir.
Mansur's overthrow is used as a pretext by Mahmud of Ghazni to conquer the remainder of Khurasan still in the hands of the Samanids.
Bektuzun and Fa'iq, together with the ruler of Kuhistan, Abu'l-Qasim Simjuri, however, are judged to be too powerful by Mahmud.
He therefore makes peace with them in the spring of 999, keeping Balkh and Herat.
The allies spoil the peace by attacking the rearguard of Mahmud's army.
Mahmud's forces remain intact, however, and hostilities resume.
Mahmud defeats the allies near Merv and subsequently seizes all land south of the Oxus.
He also gains the loyalty of Chaghaniyan and other minor states to the north of the Oxus that had hitherto been loyal vassals of the Samanids.
At this point, 'Abd al-Malik and Fa'iq (to be joined later by Bektuzun) attempt to gain enough momentum for a renewed offensive against Mahmud.
However, Fa'iq soon dies.
Meanwhile, Kara-Khanid ruler Ali bin Musa (title: Kara Khan or Arslan Khan), a cousin of the late Hasan, has resumed the Kara-Khanids’ campaign against the Samanids, and in 999 Ali's son and successor Nasr launches an invasion.
Faced with the hostility of his subjects, 'Abd al-Malik is helpless against the Turkic onslaught.
Bukhara is occupied without a struggle, and 'Abd al-Malik is taken prisoner.
Although 'Abd al-Malik's brother Isma'il Muntasir will temporarily regain some of the Samanid lands in the following years, the Samanid state is effectively abolished.
The Samanid domains are split up between the Ghaznavids, who gain Khorasan and Afghanistan, and the Karakhanids, who receive Transoxiana; the Oxus River thus becomes the boundary between the two rival empires.
