The Herat campaign of 1862–1863 was a conflict between the Principality of Herat and the Emirate of Afghanistan, from March 1862, when Sultan Ahmad Khan captured Farah from the Muhammadzai Emirs and continued through the 10-month long siege of Herat, ending on May 27, 1863, when the city fell to the Amir-i Kabir, thus completing the unification of Afghanistan.