Complex sentence: It went from Central Asia to the Caspian Sea to the Black Sea, which allowed no contact with Persia; however, some caravans loaded with silk did pass through Persia to reach the Empire.
Split into simpler sentences: It went from Central Asia through the Caspian Sea to the Black Sea, avoiding all contact with Persia. Some caravans loaded with silk did, however, pass through Persia to reach the Empire.