Complex sentence: Kakhovsky was sent to the 7th Ranger Regiment to fight in the Caucasian War, where he had made a fast career: in November 1817 he became a Junker, in 1819 he became a poruchik, in 1821 he retired from army because of an illness.
Split into simpler sentences: Kakhovsky was sent to the 7th Ranger Regiment to fight in the Caucasian War. There he had made a fast career: in November 1817 he became a Junker, in 1819 he became a poruchik, in 1821 he retired from army because of an illness.