There is a number that ought to concentrate the mind: thirty-nine trillion dollars. That is the gross federal debt of the United States as of the eighteenth of March 2026, a figure that crossed this particular threshold in the same week that American aircraft were striking targets in the Zagros Mountains and Iranian mines were drifting in the shipping lanes of the Strait of Hormuz [1]. The coincidence of these two facts is not merely dramatic; it is, in a fiscal sense, consequential. The Congressional Budget Office estimated the federal deficit for fiscal year 2026 at $1.9 trillion before the conflict began [2]. The war, by the most conservative available estimate, is adding approximately one billion dollars per day to that figure, a sum that, if the conflict were to last sixty days, would produce net new expenditures of roughly $65 billion, plus $1.4 billion in additional interest costs on the borrowing required to finance them [3].
The arithmetic is relentless, and it is not new. What is new is the context in which it is accumulating. The United States has conducted military operations while carrying large deficits before; indeed, it has rarely done otherwise since the Korean War. But the current fiscal position is qualitatively different from any prior wartime episode in one critical respect: the debt-to-GDP ratio, which stood at approximately 100 per cent at the end of fiscal year 2024, is projected by the CBO to reach 120 per cent by 2036 even without the additional expenditures of the Iran conflict [2]. Interest payments on the existing debt are on track to exceed one trillion dollars in fiscal year 2026, a sum that surpasses the entire defence budget and is itself growing, because each increase in the deficit requires additional borrowing, which generates additional interest charges, which widen the deficit further. This is the feedback loop that fiscal economists have warned about for two decades, and it is now operating in real time, amplified by a war that no deficit hawk in Washington anticipated when the fiscal year began in October.
The bond market's response to the conflict has been, by historical standards, perverse. In every major geopolitical crisis of the past half-century, from the Gulf War through the September 2001 attacks to the invasion of Ukraine, Treasury prices rose and yields fell as investors sought the safety of American government debt. This time, the opposite has occurred. The ten-year Treasury yield, which stood at 3.82 per cent at the start of the year, rose to 4.06 per cent within days of the first American strikes and has since fluctuated around 4.3 per cent [4]. The explanation is not mysterious, but it is alarming: investors are pricing the inflationary consequences of the oil shock and the fiscal consequences of the war spending ahead of the traditional safe-haven impulse. The Treasury market is not signalling confidence in American creditworthiness. It is signalling concern about the sustainability of the borrowing trajectory, and it is doing so at precisely the moment when the government's need to borrow is intensifying.
The Treasury market is not signalling confidence in American creditworthiness. It is signalling concern about the sustainability of the borrowing trajectory, at precisely the moment when the government's need to borrow is intensifying.
The structural dynamics underlying this shift are worth examining with some care. The federal government must refinance approximately $9.2 trillion in maturing debt over the course of 2026, in addition to financing the current-year deficit. This refinancing requirement would be manageable in an environment of stable demand for Treasuries. But demand is not stable. Foreign central bank holdings of US Treasuries have declined as a share of the outstanding stock for several consecutive years, a trend that accelerated modestly in the second half of 2025 as geopolitical diversification became a stated policy objective of several major holders, including China and Saudi Arabia [5]. The war has introduced an additional complication: Iran's threat to the Strait of Hormuz has raised questions about the petrodollar system itself, the informal arrangement under which oil-exporting nations recycle their dollar revenues into Treasury purchases. If the Strait disruption persists, or if oil-exporting nations perceive American foreign policy as a source of instability rather than security, the structural bid for Treasuries from this source may weaken further [5].
The Competition for Capital
There is a further complication that has received insufficient attention. The federal government is not the only large borrower in American capital markets. Corporate bond issuance in the first quarter of 2026 has been at record levels, as firms rush to lock in financing before the conflict pushes borrowing costs higher. The resulting competition for investor capital between the Treasury and the corporate bond market is exerting upward pressure on yields across the curve [6]. This crowding-out effect, which was largely theoretical during the era of quantitative easing when the Federal Reserve absorbed vast quantities of government debt, is now reasserting itself as a practical constraint. The Fed's balance sheet, while still large, is being wound down through quantitative tightening, and the central bank has shown no inclination to reverse course and resume large-scale Treasury purchases, particularly given the inflationary environment created by the oil shock.
The Federal Reserve's own position is, in this regard, uncomfortable. The federal funds rate stands at 3.50 to 3.75 per cent, having been cut from 5.25 per cent over the course of 2025. Goldman Sachs, which had previously forecast a rate cut in June, has delayed its expectation to September at the earliest, on the grounds that the war-driven oil price increase has made the inflation outlook too uncertain for the Fed to ease further [4]. If the Fed cannot cut rates, the government's marginal cost of borrowing remains elevated, which in turn widens the deficit, which requires more borrowing, which puts further upward pressure on yields. This is the vicious circle that the CBO has been modelling in its long-term projections for years, but which the Iran war has brought forward from a theoretical future into an observable present.
Historical Parallels and Their Limits
The temptation to draw parallels with previous wartime debt episodes is strong, and the parallels are, up to a point, instructive. At the end of the Second World War, the gross federal debt stood at 106 per cent of GDP, the highest ratio in American history until, the CBO now projects, it is surpassed sometime around 2030 [2]. The post-war reduction of that debt ratio was achieved through a combination of robust economic growth, moderate inflation, and financial repression: the Federal Reserve maintained an interest rate cap on government bonds from 1942 to 1951, effectively compelling banks and savers to hold Treasuries at below-market yields. The conditions that enabled that debt reduction, a baby boom, rapid industrialisation, global demand for American exports in a war-ravaged world, and a captive domestic investor base, are not present today and will not be present tomorrow.
A closer parallel, and a more troubling one, is the fiscal trajectory of the United Kingdom in the 1960s and 1970s, when the costs of maintaining a global military posture collided with a weakening domestic economy and persistent inflation. The result was a sovereign debt crisis that culminated in the humiliation of the 1976 IMF loan, an episode in which the world's former reserve currency issuer was forced to accept external conditionality in exchange for emergency financing. No responsible analyst would suggest that the United States is approaching such a moment; the dollar's reserve currency status, the depth of American capital markets, and the absence of a plausible alternative reserve asset all provide buffers that post-imperial Britain did not possess. But the direction of travel, if not the destination, is recognisable: a great power discovering that the fiscal cost of its geopolitical commitments is growing faster than the economic base from which those commitments are financed.
The Committee for a Responsible Federal Budget observed in a March analysis that the federal government had already accumulated a deficit of one trillion dollars in the first five months of fiscal year 2026, before the war began [7]. The CBO's latest long-term projections, published in early March, forecast cumulative deficits of $24.4 trillion over the coming decade, with annual deficits exceeding $3 trillion by 2036 [2]. These projections incorporate assumptions about economic growth and interest rates that may prove optimistic if the conflict in the Middle East persists or escalates. The thirty-nine trillion dollar debt figure, in other words, is not a ceiling. It is a waypoint.
What the bond market is pricing, and what the fiscal data confirm, is that the United States has entered a period in which the interaction between its military commitments, its fiscal position, and its borrowing costs is no longer a matter for long-range projections but for immediate policy. The war in Iran has not created this dynamic; it has accelerated it. The federal debt would have continued to grow in the absence of any conflict, driven by the structural mismatch between mandatory spending commitments and revenue. But the war has compressed the timeline, adding billions in unbudgeted expenditure at a moment when the market's willingness to absorb additional supply is visibly declining. The question that remains is not whether the fiscal trajectory is sustainable; the CBO has answered that question definitively in the negative. The question is what, if anything, the political system is prepared to do about it, and the answer, to judge by the silence on Capitol Hill regarding war appropriations, is: not yet anything at all.
- "U.S. National Debt Soars Past $39 Trillion Amid Concerns Over Cost of Iran War." Time. 19 March 2026. time.com
- Congressional Budget Office. "The Budget and Economic Outlook: 2026 to 2036." CBO. March 2026. cbo.gov
- "Trump's Iran war could hike national debt by $65 billion in 60 days, while tariffs add another crushing blow." Fortune. 12 March 2026. fortune.com
- "10-year Treasury yield tops 4.06% as surging oil prices from Iran conflict raise inflation angst." CNBC. 3 March 2026. cnbc.com
- "Iran, the $39 trillion national debt and dedollarization: How Trump exposed America's Achilles Heel in Hormuz." Fortune. 24 March 2026. fortune.com
- "U.S. debt is competing with a record supply of corporate bonds, pushing up the cost of federal borrowing just as war spending piles up." Fortune. 16 March 2026. fortune.com
- "CBO Estimates $1 Trillion Deficit for First Five Months of FY 2026." Committee for a Responsible Federal Budget. March 2026. crfb.org