Complex sentence: Ottoman Bessarabia was annexed by the Russian Empire in 1812, along with all Moldovan territory east of the Prut river, which the Russians governed jointly in one single Russian province of Bessarabia.
Split into simpler sentences: Ottoman Bessarabia was annexed by Imperial Russia in 1812, along with all Moldovan territory east of the Prut river. The Russians governed these territories jointly in one single Russian province of Bessarabia.