I think it's more to do with the fact that China has a monopoly on most rare earth metals, and the supply can get constrained, like they did last year against Japan.
Nitpick: China doesn't have a monopoly on rare earth metals, they just have the least restrictive policies on mining them, and they won't export the raw materials which forces companies to bring their processing operations into china.
The US has plenty of rare earths, they just always come up with thorium, which regulators regard as a nuclear waste that must be disposed of at exorbitant cost to the mine operators.
Actually, there are a number of places with large Lanthanoid deposits, but since China was supplying them so cheap, the mines were not economical. Now that China is tightening supplies, they have reopened the California mine in Mountain Pass that used to be a major supplier.
As others have stated, China does not have a monopoly, but they do supply 95% of rare-earth metals, and have been buying mines in other countries, which is leading to a monopoly type situation.
