China fell low thanks to external sabotage (opium) and espionage (stolen tea,spices,manufacturing processes) by 5+ of the future economic powers working together in the take down of the superpower. This attack and disruption of established Chinese/Indian trade routes allowed new Western industrial manufacturers to step in and supply the market.

The US/UK has had anti-Chinese policies since the early 1800s leading to the modern day (people we celebrate were some of the biggest opium dealers in the world). Teddy Roosevelt (inheritor of a drug dealing fortune) even used the Japanese to sabotage China again when he was president in 1900s when he authorized Japanese expansion into Asia with a secret treaty.