Why was trade so poor during the Middle Ages ?

10 points per question and brainlist 1. name four of the ruling dynasties of china. describe at least three contributions to society from each dynasty. 2. why did the qin ruler zheng burn chinese literature and philosophy books? how did the han dynasty establish a strong and effective government? why did people rebel against the sui rule? 3. what new technologies were invented during the tang dynasty and fully developed in the song dynasty that would eventually have a great impact on the world? explain why this technology had such an impact. 4. who were the invaders that seized control and took over the song dynasty? 5. how was china's history affected by its policies of isolation from the outside world during the ming dynasty?