This is an interesting question. My take: I do not quite accept the notion that China did not seek to "weaponize" rare earths and instead stumbled into a position of advantage. For at least 16 years, and likely more, the purpose has been an economic weapon. This is not like, say, solar or EVs, where excess capacity is sort of an accident. Here, for example, is a semi-authoritative book cited by @JohnF_Sullivan on rare earth strategy written in 2011 for the state China Economic Publishing House the year after the Japan situation: "What magical quality do rare earths possess that makes the usually arrogant and domineering Americans so furious? What magical quality do rare earths posses that leaves the usually wealthy and arrogant Japanese grief-stricken? China is the only country in the world capable of supplying all 17 rare earth elements, particularly holding a larger share of heavy rare earths that have prominent uses in military applications. To change China’s international position in the rare earth industry, since 2009, the Chinese government has launched a vigorous rare earth defense war, adopting a series of rectification measures including suspending approval of mining rights, controlling total mining volume, reducing export quotas, raising export tariffs and and severely cracking down on rare earth smuggling." A key purpose of these post-2009 steps, which PRECEDE China's weaponization against Japan in 2010, was to hone a better coercive instrument. Then there is some empirical evidence suggesting PRC action in this sector was about leverage. First, most obviously, China used this as a coercive instrument in 2010. That shows, for at least 16 years, they have understood it as a critical leverage point. Second, China's government has for decades manipulated the price of rare earths to prevent anyone else from achieving scale - dropping the price to kill foreign investment. Why did they do this when they already had 90% market dominance? The logic is toward control, not profit, and it is not the result of disaggregated independent Chinese market actors (which do not exist in this sector). Third, related to that point, if this industry operated on economic logic, we would probably see more fragmentation. Indeed, for a brief time, we did see that before 2010. But then the PRC sharply consolidated the rare earths industry into state-backed companies. They shut down, arrested, harassed, and outright expropriated private actors. This was partly to ensure greater state control over external flows - the better to maintain leverage. The quote above refers to that effort. Fourth, I do not think China's controls on rare earth minerals were modeled off U.S. controls. For example, the October controls went far beyond any U.S. controls. China's idea was any product, anywhere in the world, with .1% value coming from Chinese produced rare earths, required a license to be sold to anyone else in the world. The closest analogy -- and Chinese scholars have said this directly -- is to U.S. financial sanctions, not export controls. Fifth, this is not a case where "there are many different actors, and they often overperform in search of particular targets." The industry has for a long time just been a few actors, tied to the state, acting at the state's direction. China's cultivation of leadership in this sector dates back to the 1960s, accelerating in the 1980s, with direct involvement of Deng's family in the 1990s and Premier Wen in the 2000s. The empirical evidence seems to indicate a conscious desire to dominate this sector. One can debate whether or not such an intention was justifiable given U.S. control over chokepoints like finance. But I think it is hard to advance the claim this was just the independent action of market participants that happened to accidentally create a position of extreme concentration and dominance.