The siege of Herat (1837–1838) was an attack on the Principality of Herat by Qajar Iran during the Great Game. Herat was held by Kamran Shah and his vizier Yar Mohammad Khan Alakozai. The Shah of Persia was Mohammed Shah Qajar. Four Europeans were involved: the British, Sir John McNeill and Eldred Pottinger as well as the Russians, Count Simonich and Yan Vitkevich. Sher Mohammad Khan Hazara, an ally of Kamran and chieftain of the Qala-e Naw Hazaras, helped form a Sunni Confederacy of Aimaq, Turkman, and Uzbek tribes and played a crucial role in defending Herat during the early days of the siege. The siege ended when neither side gained a clear advantage, the British threatened to take military action and the Russians withdrew their support.