The Monroe Doctrine had first established American isolation and it remained so until WW 1 and for the 20 years after they attempted to restore that, however after the unrestricted submarine warfare the Germans used lead to the U.S finally entering WW 2
The answer that best applies to both the Tang and Song dynasties would be C. A Reliable food production and distribution system. This gave both dynasties the ability to thrive.
The 1920's saw a period of rapid industrialisation, which made the decade to be correctly called the Roaring twenties. However, it is only the industrialists who benefited from the boom, with the majority of the working population conditions remaining poor. This was a fragile situation that led to the great depression as few money was circulating in the larger population. This has led to some conspiracy theorists attributing the blame of the great depression to the industrialists and bankers.
A lot of people don't understand sarcasm, and some get offended.