China is the world leader when it comes to rare earths. This can be used this as leverage in a trade war with the U.S.

From morningstar.com

China leads the world when it comes to the production and processing of rare earths. That may be a key weapon in its trade battle with the U.S. - and its move to expand export restrictions on those elements shows that China knows it. The U.S., meanwhile, has been taking small steps to ease its reliance on Beijing for these critical materials, making China's efforts to tighten control of the market a little less effective. The country's "rare-earth dominance remains its most visible pressure point in the trade conflict - a weapon that can sting, but not guarantee victory," said Stephen Innes, managing partner at ... (full story)