Who invaded and conquered russia in the thirteenth century and with what result? a. mongols; whole populations were killed, treasures were looted, and cities were leveled. b. chinese hordes; serfdom expanded, taxes went up, and thousands of people were killed. c. byzantines; government became more efficient, many russians adopted byzantine customs, and the invaders gained trust. d. muslims; many russians converted to islam, and arabic art, science, and architectural styles were introduced.