A) china was a very weak country
1) chinese were the lowest class in mongol, manchu, xianbei, Khitan, Jurchen empires.
genghis khan's law, killing a chinese = killing a donkey,
sorry to mention this
mongols, manchs, xianbei killed over 50% of chinese. (in three different times)
2)jurchen took two chinese kings, and forced them walk naked trough the streets of the capital of jurchen empire,
chinese kings had to call the kings of jurchen as uncle for about 100 years.
Men of chinese royal family were sold into slavery in exchange for horses with a ratio of ten men for one horse.
http://en.wikipedia.org/wiki/Jingkang_Incident
3) chinese king had to call the Khan of Khitan as father, grandfather
http://en.wikipedia.org/wiki/Later_Jin_Dynasty
4)other two chinese kings of chinese were also take by foreigners as slaves.
http://en.wikipedia.org/wiki/Emperor_Huai_of_Jin
5) manchus ruled china for 300 years till 1911.
the population rate was 100,000,000 chinese VS1.000.000 manchus.
5)then japan ruled 2/3 of china since 1937-1945( including the chinese captial), and killed over 30,000,000 chinese.
Russia and USA saved china , Otherwise china should ruled by japan now.