 In 1805 Buxhoevden took part in the Battle of Austerlitz as a commander, contributing to the Third Coalition's failure to defeat Napoleon by being drunk during the battle.In 1808 he served as Commander-in-Chief in the Russian conquest of Finland, and led Russian troops during the initial battles of the Finnish War (1808-1809).Buxhoevden received the castle and lands of Koluvere in western Estonia after Duchess Augusta of Brunswick-Wolfenbüttel had died there in 1788 in suspicious circumstances.