Inside the 'yen-tervention': Why the US stepped in to boost Japan's currency

• The US and Japan staged a dual intervention for the yen for the first time since 1998.
• Detailed below is what both sides got out of it, and what's next for investors.
• Sign up for First Trade, Business Insider's daily markets newsletter.

I was recently watching a pickup basketball game that my son was playing in with his friends. It was a lopsided affair, with my son's team running away with it.

Players on both sides seemed frustrated. The losing team was withdrawn and the leading team was getting bored. The game was fizzling.

So I did what any former-athlete dad would do: I hopped onto the losing team. Suddenly we were cooking. A few made baskets later, the game was a lot more even.

My intervention was a roaring success in some ways. I revitalized a game when the intensity was flagging. But there were some drawbacks, too. The result was in the right direction, but the game suddenly wasn't about the kids anymore. Everyone was forced to react to the biggest player on the floor.

Imagine this scenario playing out at the highest level of markets and geopolitics. Well, it just happened in the global currency market.

For the first time since 1998, the US and Japan teamed up to push the yen higher. This ultra-rare intervention shares a lot of DNA with my basketball-game invasion: it was mutually beneficial, and designed to stem a situation that was getting out of hand.

But the stakes are, of course, much higher when it comes to the $9.5 trillion currency market. Here are the major considerations for investors:

How did the yen get into this mess?

The lowest yen in 40 years versus the US dollar doesn't just happen overnight. The biggest culprit has been the widening gap between the Federal Reserve and the Bank of Japan. Higher US rates have made dollar-denominated assets far more attractive to global investors.

That interest-rate differential has fueled the carry trade, in which investors borrow cheap yen to invest in higher-yielding assets elsewhere. As more investors sell yen to buy foreign assets, the Japanese currency comes under even more pressure.

More recently, renewed tensions in the Middle East have put additional downward pressure on the yen by boosting demand for the safe-haven US dollar.

What's in it for the US?

A collapsing yen isn't just Japan's problem. It encourages massive carry trades that can spill over into markets worldwide if they unwind suddenly. Washington ultimately decided the game had become too lopsided to keep watching from the sidelines. It was essentially playing defense against global financial instability.

A weaker yen also makes Japanese exports cheaper relative to US goods, potentially widening trade imbalances.

In addition, defending the yen can also require Japan to tap its vast Treasury holdings to raise dollars. Large-scale Treasury sales could put upward pressure on US yields — another outcome Washington would prefer to avoid.

What's in it for Japan?

Japan has a more direct problem: a weak yen raises the cost of imported energy, food, and raw materials, squeezing businesses and households.

There's also the matter of credibility. Left unchecked, a falling currency can become a self-fulfilling prophecy as investors pile into bets against it. By teaming up with the US, Japan isn't just buying yen — it's also messaging that it's willing to defend its currency with one of the world's most powerful financial partners at its side.

What's next?

The history of joint interventions is actually quite promising. They tend to be more credible and longer-lasting. A previous US-Japan collaboration in 1998 helped stem a sharp yen decline, while the Plaza Accord in 1985 saw the US, Japan, West Germany, France, and UK band together to catalyze a prolonged decline in the dollar.

That being said, the market still cares about fundamentals. The US-Japan interest-rate gap isn't going anywhere, and the carry trade isn't going to disappear overnight.

After all, stepping onto the court can stop the bleeding. But staying competitive in the long run requires changing how the game is played.

The post Inside the 'yen-tervention': Why the US stepped in to boost Japan's currency appeared first on Business Insider