The US has become dependent upon imported natural resources. For example, once we were a net exporter of oil. During WWII, US oil helped the allies to victory. The axis had scant oil, and was not able to field enough planes, ships, and tanks to win. However, our conventional oil became substantially mined out. Recently,
US oil production has improved. However, companies mining unconventional oil are not really making enough profit to fund needed investment in infrastructure. Its mostly been creative accounting used to justify loans.
The US is also dependent upon imported potash to keep our farms productive. Many other minerals are needed to keep machines productive. The whole point of empires during the 20th century was to give European nations a monopoly on importing natural resources from their empires. Imported natural resources allowed them to produce myriad products in their factories, and dominate the globe. Natural resources are needed as input for machines to produce products, and there are no more empires. Nowadays, its mostly those who produce trade goods more efficiently than the competition who get to import resources. Anyone can compete.
If China has a 50% savings rate, they can build a lot of new factories. If the west has a zippo savings rate, they have to borrow capital from others to build factories. There is talk of the west converting to a "service" economy, but that's just another way of saying going back to doing things by hand. There is a reason the US was only able to gather the resources to design one type of warplane (F-35) this generation, compared to myriad specialty warplanes in days of yore. The US just doesn't produce 50% of global GDP anymore like it did during WWII. "Service economy" means producing relatively few goods and services by hand, instead of multiplying the efforts of individuals with machine helpers.