Why was there a general breakdown in political order between 8th and 3rd century
b. c.e.?

There was a time in the 8th century B.C.E. when the Zhou Dynasty’s ability to control its vassals broke down internal conflicts made China vulnerable to invaders outside their lands. It was also in the 8th and 3rd centuries B.C.E. when nomadic people made some drastic moves by raiding farming areas of the North China plain. There were others who settled and taken some captured existing states. There were also rivalries between lands, signals of resistance, revolts, conflicts, war and invasion. Despite all of these, there were also actions made for the intention of the consolidation of Chinese civilization which resulted to a distinct Chinese culture and identity which emerged and carried the Chinese people through the difficult times. 

yes i think there would be volunteers