Currency intervention is rarely about friendship

CURRENCY intervention is rarely about friendship. The United States did not join Japan in propping up the yen because it felt sorry for Tokyo's import bills. It did it because the alternative - Japan, the world's largest foreign holder of American government debt, being forced to sell Treasury bonds to defend its own currency - threatened to spike American borrowing costs at precisely the wrong moment. The coordinated operation last week, the first US-Japan joint intervention to buy yen since 1998, was an act of American self-preservation disguised as alliance solidarity.

The yen had fallen to 163.73 per dollar on Thursday, its weakest level since 1986, before bouncing back to roughly 157 after authorities acted. The dollar index, which measures the greenback against a basket of six currencies, slid to 99.8 at the start of August, its lowest point in seven weeks. Much of the dollar's retreat was not caused by the yen alone. Oil prices tumbled on growing optimism that the United States and Iran could reach a deal to reopen the Strait of Hormuz, reducing inflation fears and trimming the market-implied probability of a September Federal Reserve rate hike. With Brent crude falling more than 5% and the Fed's divided July meeting - a 9-3 vote, with three members wanting a quarter-point increase - the dollar found itself under pressure from both sides.

To be sure, the intervention has had an effect. Japan's finance ministry and the Treasury have vowed not to hesitate in acting again. The United States also signalled it would consider upsizing the Federal Reserve's FIMA repurchase facility, a programme that lets foreign central banks borrow dollars against Treasury collateral rather than selling bonds outright. That detail matters more than the headline. By assuring markets that Tokyo can raise dollar liquidity without dumping Treasuries, Washington addressed the specific mechanism that could have transmitted yen weakness into American funding markets. Masahiko Loo, a senior macro strategist at State Street, observed that the signal about the FIMA facility "may be bigger than the intervention itself."

Yet the fundamentals that pushed the yen to a 40-year low have not shifted. Short-term interest rates remain roughly 2.5 percentage points higher in the United States than in Japan. The Bank of Japan held its policy rate steady at 1% at its latest meeting, though it signalled that further tightening was coming. Even its June rate hike - the first increase in years, to a 31-year high - barely moved the currency for long. Solo intervention in April and May produced only a transient rebound. The gap between Japanese and American borrowing costs is the engine of yen depreciation, and no amount of verbal warnings from finance ministries closes it. Robin Brooks of the Brookings Institution put it plainly: Japan's monetary framework is full of contradictions, with the BOJ buying 2.5 trillion yen of government bonds each month to suppress long-term yields while the finance ministry intervenes to strengthen the yen.

The deeper problem is that the yen's weakness has become embedded in global financial plumbing. A persistently cheap yen has fuelled the so-called carry trade - investors borrow in yen at low rates and deploy the proceeds into higher-yielding assets, from American tech stocks to emerging-market bonds. HSBC estimates that carry trades total more than $1 trillion. When the yen unexpectedly strengthened in 2024 following a surprise BOJ rate hike, the resulting unwind triggered a global market rout, with the worst day for Japanese stocks since 1987. The US intervention, by establishing a floor around 160 yen and signalling resolve, kept those bets alive rather than forcing a reckoning. That is arguably the point. But it also means the system remains vulnerable to the next shock.

The dollar's retreat complicates the picture. A weaker dollar ordinarily eases pressure on the yen, since the two currencies are mirror images of one position. Mideast diplomacy - or at least the hope of it - has pulled the dollar down on multiple fronts. The Iran conflict, now in its sixth month, has whipsawed crude prices: Brent reached more than $126 a barrel in April before falling below its pre-war level of $72, then surging 24% in July as hostilities flared again. Any credible deal to reopen the Strait of Hormuz removes the risk premium from energy markets and, by extension, from American inflation. Job openings fell to 7.36 million in June, factory orders declined for a second consecutive month, and core consumer inflation slowed to 2.6% year-on-year. These data points have pushed back the urgency for a September rate hike. But the US dollar index is still above 99, and rate futures continue to price a majority chance of tightening. The dollar's retreat is a correction, not a capitulation.

The stronger the yen becomes, the more the carry trade faces a squeeze. Goldman Sachs has argued that the most powerful long-term support for the yen would come not from intervention but from Japanese investors repatriating some of the trillions of dollars they hold abroad. That would require a conviction that the yen is headed higher and that domestic returns are improving - a circular dependency that only monetary tightening can truly resolve. The BOJ's next policy meeting in September is therefore the real test. If Governor Kazuo Ueda's bank raises rates to 1.25% as many analysts expect, it narrows the interest-rate gap and gives the yen structural support beyond the next intervention. If it does not, the floor at 160 yen will prove to be a speed bump rather than a wall.

The geopolitics of the move should not be ignored. A coordinated intervention sends a message to Beijing about alliance cohesion, as Jesper Koll of Monex put it: "China's leadership cares about actions, not words". The United States has also repeatedly argued that the yen is substantially undervalued, giving it a trade-policy incentive to correct what it sees as an unfair competitive advantage for Japanese exporters. But treating the yen as a currency-war pawn risks undermining the very intervention the US orchestrated. If Washington wants a stronger yen for trade reasons but also wants the carry trade to keep flowing into American assets for liquidity reasons, it faces a policy contradiction. It cannot have it both ways indefinitely.

The broader lesson is that currency intervention is a temporary analgesic, not a cure. It buys time for central banks to adjust policy without triggering a disorderly market repricing. What happens after the painkiller wears off depends on monetary arithmetic, not political statements. Japan needs higher rates. The BOJ knows it. The question is whether it can raise them fast enough before the next Mideast flare-up sends oil prices - and inflation - higher again, forcing yet another intervention.

The US saved itself from a Treasury sell-off. Japan saved its currency from a further fall. Neither country has fixed the structural imbalance that caused the problem. That bargain is breaking.