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.