Buying the yen does not make you friends with Japan

JAPANESE diplomats will relish the headline. Currency markets will be less sure what to make of it.

On Friday July 31st the Federal Reserve's New York branch sold euros to buy yen on behalf of the Treasury, through Goldman Sachs and Morgan Stanley, according to the Financial Times. The operation came a day after Japanese authorities themselves had spent up to $59bn buying their own currency, central-bank data showed. Together this marks the first coordinated US-Japanese currency intervention since 2011, when both nations pooled resources to steady markets after the earthquake and tsunami. The yen had fallen to its weakest level against the dollar since 1986, trading near 159 yen to the dollar. Japanese Finance Minister Satsuki Katayama is expected to announce the joint action on Monday.

The photograph that tells the story is not of a handshake. It is of a notepad. At a cabinet meeting at Camp David on Friday morning, Treasury Secretary Scott Bessent was seen with an underscored scribble: "Buy Japanese Yen (JPY) $5-10 bil." Mr Trump, for his part, framed the intervention as a gesture of friendship. "For nearly 80 years the American and Japanese people have enjoyed a friendship like few others," he said after meeting Prime Minister Sanae Takaichi at the White House in March. The currency rescue is the latest proof, the administration would have you believe.

Friendship is a warm word. The incentive structure is less sentimental.

The reason is not hard to see. In July 2025 Mr Trump extracted what he called the "largest trade deal in history" from Japan: a commitment of $550bn in Japanese investment directed by the United States toward American industry, in exchange for a "moderate" 15% reciprocal tariff on Japanese imports. The deal also secured Japanese purchases of 100 Boeing aircraft, billions in US defence equipment, greater access for American agriculture, and the lifting of longstanding restrictions on US cars. A second tranche of investments was announced in March this year, including up to $40bn from GE Vernova Hitachi for small modular reactors in Tennessee and Alabama, and $33bn for natural gas facilities in Pennsylvania and Texas.

A collapsed yen would put that architecture at risk. The weaker the yen, the harder it is for Japanese companies and finance institutions to deploy $550bn of new capital abroad. The weaker the yen, the more Japan's own economy deteriorates through import inflation, shrinking real incomes and a consumption spiral. And a Japanese economy in freefall is not one that can sustain the defence spending increases, technology partnerships and Indo-Pacific commitments Mr Trump also wants from Tokyo. The intervention is less an act of charity than a maintenance payment on an asset.

To be sure, the US has a genuine interest in an orderly yen. Carry-trade unwinds - where investors borrow in low-yielding yen and invest in higher-yielding dollar assets - can cascade when the yen strengthens abruptly, as it did in 2024 when a sudden reversal sent global equity and credit markets into a brief but sharp disarray. The Federal Reserve has a vested interest in preventing precisely that kind of disorder. But the Fed's own monetary policy is also part of the problem: with American interest rates far above Japan's, the yield differential is the fundamental driver of yen weakness. The Bank of Japan left policy unchanged on Friday but signalled a rate hike is likely, which would narrow that gap. Any lasting fix requires the Bank of Japan to move, not just Treasury desks in New York.

The mechanics of the intervention itself are revealing. The US did not sell dollars to buy yen - it sold euros. That is a telling detail. Selling euros means the Treasury is working within its existing foreign-exchange holdings rather than expanding its dollar liability. It also means the dollar itself is not being weakened to prop up the yen. The arrangement is surgical: support Tokyo's currency without sending a message to other trading partners that Washington will routinely subsidise their exchange rates. The $5bn to $10bn indicated on Mr Bessent's notepad is a modest sum in currency-market terms. Its purpose is partly signalling.

Yet there is an irony that neither side can entirely disguise. The United States just spent two years threatening Japan with tariffs to bring it to the negotiating table. The headline now is that the same government is buying Japanese currency to save it from collapse. To the casual observer the position looks inconsistent. In practice it is perfectly coherent. Tariffs and currency interventions are not contradictory tools; they are complementary ones. Tariffs pressure Japan's trade balance and force investment commitments. Currency support prevents the Japanese economy from deteriorating to the point where those commitments become impossible. The first squeezes. The second ensures there is something left to squeeze.

The trouble is that this approach contains a structural tension. A weaker yen makes Japanese exports cheaper, which partially offsets the tariff's intended effect on the US trade balance. A stronger yen, meanwhile, helps Japan's consumers and importers but hurts its exporters - precisely the companies the US wants investing in America. The two objectives can be aligned only so far. The yen cannot be both strong enough to make the 15% tariff bite and weak enough to keep Japanese exporters competitive.

Japanese authorities know this. They have intervened repeatedly, not least in April this year, only to see the yen sell off again. As one market analyst on Substack pointed out, the fundamental drivers - the interest-rate differential, the US economy's relative strength, Japan's persistently low yields - have not changed. Interventions without monetary-policy adjustment are a stopgap. The Bank of Japan needs to raise rates, and it needs to do so credibly. Until then, both Tokyo and Washington are burning cash on a hill they cannot permanently defend.

The broader lesson is about the shape of American power under Mr Trump's trade policy. The old model of American influence relied on open markets and multilateral rules. The new model blends coercive tariffs with selective bail-outs, bilateral investment extraction with alliance reassurance. It is more transactional. Whether it is more effective is an open question. The Japan deal looks impressive on paper - $550bn in investment, market access for Boeing and American farmers, a 15% tariff that is less than the 24% initially threatened. But the fact that the US now needs to prop up its ally's currency to keep the deal alive suggests the architecture is more fragile than the rhetoric implies.

Friendship, in international economics, is what you call mutual interest when the optics demand warmth. The yen intervention is not evidence of affection. It is evidence that both nations recognise their fate is tied together - and that Mr Trump's tariffs, for all their bluster, have not entirely replaced the older, less theatrical forms of alliance management. The smarter question is whether this blend of coercion and subsidy can be sustained when other trading partners - the European Union, South Korea, China - still await their turn at the negotiating table.