When exchange rates become a geopolitical tool: The US and Japan join forces to "weaponize" the yen, forcing the market to rewrite its pricing formula.

The unprecedented joint intervention by the United States and Japan to support the yen may profoundly influence future market behavior patterns. Japan has intervened in the foreign exchange market in the past, but the scale of this action far exceeds previous efforts. More critically, this intervention has received public backing from the United States; reports indicate that the intervention was executed not directly through the dollar-yen pair, but rather via the euro-yen cross, accompanied by clear political support signals. Some investors view this move as highly significant. "The Japanese Ministry of Finance and the U.S. Treasury have successfully weaponized the yen," said Jesper Koll, chief strategist at Monex Group, noting that this essentially serves as a deterrent to the market. He believes that this intervention has transcended traditional foreign exchange management, as both countries have coordinated their public balance sheets to guide market sentiment. He added, When two major sovereign nations concentrate their increasingly scarce national resources on the same objective, the market has to face this signal. This joint intervention marks the first coordinated purchase of yen by the U.S. and Japan since 1998, and the first such collaboration since the Group of Seven (G7) took coordinated action to lower the yen after the 2011 Great East Japan Earthquake. Political Tool Koll also pointed out that the political signaling aspect of this action is unprecedented. By combining political support with financial firepower, the U.S. and Japan intend to raise the costs of shorting the yenplacing the balance sheets of both sovereign nations on opposite sides of the trade. Cornell University professor Eswar Prasad views this more as a defensive measure, but he also acknowledges that this operation signals an increasing intertwining of exchange rate policy with geopolitical factors. "Currency market interventions are clearly taking on geopolitical hues," Prasad stated, noting that the Trump administration appeared more inclined to support central banks deemed aligned with U.S. priorities. Some analysts draw parallels between this situation and U.S. support of the Argentine peso under President Javier Milei during a time of heightened currency volatility before critical midterm elections. In September and October 2025, the Trump administration intervened with a comprehensive package of support, utilizing the Treasury's Exchange Stabilization Fund (ESF) and conducting a $20 billion currency swap with the Argentine central bank, while also purchasing pesos in the open market. "Bassent is a key figure throughout this. The same Treasury, the same ESF, the same playbookusing foreign exchange operations as a tool of foreign policy," said Michael Gayed, chief investment strategist at Tactical Rotation Management. "The support for Argentina was to bolster an ally." Similarly, Quantum Strategy strategist David Roche stated that U.S. motives likely extend beyond financial stability or the bond market; political considerations may also be significant. "He might just want to do a favor for his ally, Takeda Sanae." The U.S. Treasury did not respond to requests for comment. Strategists believe that this intervention will change how investors think about the yen. "This will particularly alter the cost logic of funding in carry trades," said Billy Leung, investment strategist at Global X ETFs. "If investors now view the risk of intervention as a realistic and coordinated threat, they are likely to be more cautious about aggressively shorting the yen and instead seek alternative funding currencies." For a long time, the yen has been the preferred funding currency for global carry tradesinvestors borrow low-interest yen to invest in higher-yielding overseas assets. Leung added that the broader implication is that "exchange rate policy itself," after lying dormant for a decade, has re-emerged as a source of market risk. If investors gradually shift towards other funding currencies like the euro, it could reshape the positioning landscape of major foreign exchange markets. Masahiko Loo, senior fixed income strategist at State Street Global Advisors, also believes that this incident signifies that traders must increasingly incorporate geopolitical variables into their pricing. "The biggest change is that traders now have a new variable to price inpolicy reaction functions, not just macro fundamentals."