The ganges in india and chang jiang (yangtze) in china are river valleys important for the production of

I believe the answer is: Rice

In order to grow good quality rice, the field needs to have constant irrigation in order to maintain the humidity in the rice field.
Ganges and Yangtze served as the source of water that the rice farmers use to irrigate the ricefield.

Ongoing civil wars western roman empire finally collapsed476 c.e. romulus, the last of theroman  emperors in  the west, was overthrown by the germanic leader odoacer, who became the first barbarian to rule in rome. the order that the  roman empire  had brought towestern  europe for 1000 years was no more.