Osten-Sacken was only two when his father died and spent his childhood in near-poverty. He entered the
Koporye Musketry regiment as a sub-
ensign on 18 October 1766. In 1769, during the
Russo-Turkish War, 1768–1774, he participated in the blockade of
Khotin and in other engagements. For his military valour he was promoted in September of the same year to ensign and in 1770 to second-
Lieutenant. From 1770 to 1773 he served in the Nasheburgsky Musketry regiment under command of
Alexander Suvorov and fought against the
Bar Confederation. In 1786 he became a
lieutenant colonel and was appointed to the Moscow
Grenadier regiment, serving there until 19 July 1789. He was then assigned to the
Rostovsky Musketry regiment and fought in the
Russo-Turkish War, 1787–1792. For his contributions during the battles at the
Prut River and the taking of
Focşani he was awarded the
Order of St. Vladimir, 4th class, with ribbon. Later he distinguished himself at
Izmail and was praised by Suvorov as "one of those most contributed by his courage and discretion to gaining the complete victory over the enemy." On 10 August 1792 he was promoted to
colonel and from 1793 served with the
Chernigov Musketry regiment in Poland. For his participation in an engagement fought near
Vilnius he was awarded a
golden sword with an inscription for bravery. On 28 September 1797 he became the Chief of the
Yekaterinoslav Grenadier regiment with the rank of
major general and from 11 July 1799 with the rank of
lieutenant-general. After the
Second Battle of Zürich he was taken prisoner and interred at
Nancy until 1801. Upon his return to Russia, he commanded a reserve corps stationed in the Governorates of
Grodno and
Vladimir. ==Napoleonic Wars==