almost every China dynasties at it's peak were the most prosperous and advanced nation in the world, the PRC would not be the exception. the West thought that China was no longer a threat to them when the latter turned Communist in 1949. the Whites believed that Communism would destroy China, and they will be weak for 100 years. it turned out to be 50 years. PRC is now a powerful and rich country, not unlike the great Chinese dynasties of the past.
from the USA, Russia and the West perspective, they made a big mistake not supporting Nationalist China during the 1945-1949 civil war. they had an great opportunity to make China permanently weak by dividing China into North and South in 1949, which the two equally matched Chinas would be at war at and were heavily reliant on their allies alike to North and South Korea situation which has developed for the last 70 years. if that happened, there would be no unified and powerful China to challenge the West global hegemony today.