Complex sentence: The town appears to have been founded in the 16th century, when the Principality of Moldavia, gradually became dependent of the Ottoman Empire, and then was annexed by the Russian Empire in 1812 along with Bassarabia (eastern half of the Principality of Moldavia).
Split into simpler sentences: The town appears to have been founded in the 16th century, when the Principality of Moldavia, became dependent of the Ottoman Empire. Later it was annexed by the Russian Empire in 1812 along with Bessarabia (eastern half of the Principality of Moldavia).