Complex sentence: To the north of the Mordvins lived the Maris, to the south the Khazars and their eastern neighbors, possibly remnants of the Huns, became the Bolgars around 700 AD.
Split into simpler sentences: To the north of the Mordvins lived the Maris, to the south the Khazars. The Mordvins' eastern neighbors, possibly remnants of the Huns, became the Bolgars around 700 AD.