The Russo-Persian wars of 1804–1813 and 1826–1828 resulted in large irrevocable territorial losses for Iran in the Caucasus, comprising all of Transcaucasia and Dagestan, which made part of the very concept of Iran for centuries, and thus substantial gains for the neighboring Russian Empire.
Iran lost territory in the Caucasus during what wars in the early 1800s?
Russo-Persian wars