According to the theory of planned behavior, our behavioral intentions are determined in part by our perceptions of whether others will approve or disapprove of the behavior, our attitudes toward a particular behavior, and

The likely answer is rationality 

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.