Ehsan Khan Kangarloo (d.1262 AH / 1846 CE) was a military leader from the local Kangarloo family in Nakhchivan. During the Second Russo-Iranian War, he served as colonel of the Kangarloo regiment and border commander of the Qarabagh region. Amid the conflict, he withdrew from the Qajar administration by surrendering the strategic fortress of Abbasabad to Russian forces and subsequently aligning with the Russian Empire an action described in Qajar sources as a “great betrayal.” This study examines the circumstances and motivations behind this decision, addressing the question: under what conditions and for what reasons did Ehsan Khan shift his allegiance to Russia at the height of the war? Drawing on unpublished manuscripts of the Kangarloo family correspondence, Qajar-era chronicles, and local histories, the research employs a descriptive–analytical approach. Findings indicate that, despite receiving titles and offices from the Qajar court, Ehsan Khan’s alignment with Russia reflected his perception of a shift in Russian policy toward Muslim elites in the Caucasus, promising the restoration of political and economic privileges to local noble families. Additionally, the unfavorable experience of his father, Kalb-‘Ali Khan, with the Qajar administration and the gradual exclusion of their family from hereditary positions contributed significantly to Ehsan Khan’s estrangement from Iranian governance.