The moment the US debt crossed US$40 trillion, it stopped being a number and became a gravitational force — one powerful enough to bend Asia's bond markets, currencies and policy priorities.

Officials in Tokyo know this better than anyone. After decades of wrestling with its own debt?heavy equilibrium, Japan offers a preview of what happens when a government's borrowing needs start steering global capital flows rather than the other way around.

It's one thing for this dynamic to be afoot in Asia's No. 2 economy. It's quite another when we're talking about the globe's biggest — and the protector of the reserve currency.

The irony, of course, is that central banks and investors spent the first half of 2026 piling into dollars as a safe haven amid the Iran war. Despite the US having started the conflict along with Israel in late February, global funds raced into hyper-liquid US Treasuries.

Yet cracks are appearing fast since headlines earlier this month of the $40 trillion milestone. Last week, US 30-year Treasury yields rose to their highest level since 2007 at 5.3%. That prompted Treasury Secretary Scott Bessent's team to declare war, essentially, on bond bears.

Bessent rolled out a Treasury debt buyback program to cap surging yields. Though Bessent's "twist" gambit is ostensibly modeled after the policies of Nobel laureate James Tobin during the John F. Kennedy administration in the 1960s, it has serious Japanese echoes — and not good ones.

The narrative quickly shifted from Bessent bending markets to Trump World's will to the "bond vigilantes" handing the US Treasury its comeuppance. Famed investor Stanley Druckenmiller took to the Wall Street Journal to slam Bessent's gamble. "Governments defending prices against fundamentals always lose," he warned.

Here, Japan is Exhibit A. Since the late 1990s, one government and Bank of Japan team after another has declared war on bond bears. By 1999, the effort had the BOJ slashing official rates to zero. Next, Tokyo pioneered quantitative easing in 2001. Since then, Japan has unleashed countless financial sorties to battle investors bidding bond yields higher.

In 2013, the BOJ supersized its balance sheet. Over the next five years, it gorged on Japanese government bonds (JGBs) and stocks until its balance sheet topped the nation's $4.2 trillion economy.

During that period, in 2016, the BOJ experimented with yield-curve-control (YCC) tactics. It also introduced quantitative and qualitative monetary easing (QQE) and intensified its negative interest rate policy (NIRP) to keep JGB yields under wraps.