why does change happen during periods of economic or political stress?

during times of econimic, socail, and political stress, big changes need to be made. if everything is going fine, than everyone is happy, and noone needs to change anything. during the end of the Qin dynasty, the peasants and merchants were unhappy because of the strict leagalist laws and punishments. Therefore, when the emperor Shi Huangdi died, the peasants revolted and formed a new, more peaceful dynasty, the Han dynasty. The Han dynasties laws were much less strict and much more in line with confucious thought. They had zoos, universaties, and womans rights.
In modern times our financail market is in a crisis. Both presedentail canidates are promising change because our economy is doing so bad. because of the financail crisis America has taken up quick ways to get the market back on it's feet overnight. We have set up a huge bail out fund.