The answer is the An Lushan Rebellion. The rebellion cost the lives of hundreds of thousands. Although the Tang won the rebellion cost them their central government and the military as well as the economy.
They developed new products and inventions. And I think they started a number of new business
The <span>main industry in New England during the early colonial era was "ship building," since unlike in the agrarian South, the economy of New England was almost entirely mercantilist. </span>
As with most wars there’s been many reasons for example
Slavery in the economy and society
Abolitionist movement
And state and federal rights