古代中国的外部威胁永远来自北方,每一次打败游牧民族后,就把他们往中亚、欧洲那边赶,北方地理环境又不合适农耕,两三百年后,又有一个游牧民族发展起来
The ancient China external threats always from the north, every beat nomads,put them to the Central Asian, European side out of the north, the geographical environment is not suitable for farming, two hundred or three...