The United States has crossed a historic financial threshold: US national debt has surpassed $40 trillion for the first time. At almost exactly the same moment, Washington is facing the economic consequences of the ongoing Iran war, including higher energy prices, increased defence requirements, inflation risks and rising government borrowing costs.
The timing is politically and economically significant.
The US Treasury has doubled the size of some long-term bond buyback operations in an attempt to improve liquidity and calm a bond market unsettled by rising yields. The move came after long-term Treasury yields reached levels that had not been seen in many years.
This creates a bigger question than whether Washington can stabilise the bond market.
Is the Iran war exposing the limits of America’s ability to finance another major military conflict while carrying a $40 trillion debt burden?
The $40 Trillion Milestone Changes the Iran War Calculation
America’s debt problem did not begin with the Iran war.
The debt has accumulated over many years because of persistent budget deficits, pandemic-era spending, tax and spending decisions, social programmes and rising interest costs. Reuters reports that US federal debt has more than doubled since 2017.
But war changes the calculation.
Military operations require money immediately, while the economic benefits of any eventual strategic victory are uncertain.
The government must finance weapons, ammunition, aircraft operations, naval deployments, intelligence, logistics and military personnel. At the same time, an energy shock caused by conflict can increase inflation and make borrowing more expensive.
That means the Iran war can affect US finances through multiple channels simultaneously.
The Hidden Cost of War Is the Bond Market
The most important economic battlefield may not be in the Persian Gulf.
It could be the US Treasury market.
The Treasury relies on investors to purchase government securities to finance federal deficits and refinance existing debt.
When investors demand higher yields, Washington has to pay more to borrow.
The problem becomes particularly serious when a government already has a massive debt stock.
Reuters reports that the 30-year Treasury yield had reached a 19-year high before the Treasury announced larger buyback operations.
This creates a dangerous feedback mechanism:
More debt → higher interest costs → larger deficits → more borrowing → greater investor concern → higher yields.
The Iran war can add another layer to this cycle by increasing defence spending and creating inflationary pressure.
Why the Treasury Is Buying Its Own Debt
The Treasury’s decision to increase buybacks is important, but it should not be confused with a solution to the debt problem.
The Treasury plans to increase the size of certain long-term debt buyback operations from around $2 billion to at least $4 billion per operation beginning in September. The stated objective is to support liquidity in older, less actively traded Treasury securities.
The move immediately reassured markets.
But the underlying fiscal problem remains.
Buying back government bonds can improve market functioning, but it does not eliminate the government’s overall debt burden.
That distinction is crucial.
The Treasury can calm the market. It cannot buy its way out of structural deficits.
Iran War + Oil Shock = Inflation Problem
The Iran war adds another major risk: energy.
The conflict has already contributed to higher oil prices and increased uncertainty surrounding the Strait of Hormuz. Earlier this week, the 30-year Treasury yield rose above 5.3% as markets reacted to fading hopes of a quick resolution to the conflict and concerns about higher energy prices.
This matters because oil is embedded in almost every part of the economy.
Higher energy prices can raise:
- Transportation costs
- Manufacturing expenses
- Food prices
- Airline costs
- Electricity and heating costs
- Consumer inflation
- Corporate operating expenses
The Federal Reserve then faces a difficult choice.
If inflation remains high, cutting interest rates becomes harder.
If interest rates remain high, government borrowing becomes more expensive.
That is the Iran war’s financial dilemma for Washington.
The Federal Reserve Cannot Solve a Fiscal Problem
Another major misconception is that the Federal Reserve can simply cut interest rates and make the debt problem disappear.
It cannot.
If the Fed lowers rates while oil-driven inflation remains elevated, investors may worry that inflation will remain above target.
If the Fed keeps rates high, Treasury borrowing becomes more expensive.
Recent Federal Reserve meeting minutes showed that several policymakers had considered the possibility of raising rates, reflecting continuing concern about inflation.
Therefore, Washington is facing a three-way tension:
War spending + inflation + high interest rates.
The combination is much more dangerous than any one of these factors individually.
Could the Iran War Accelerate America’s Debt Problem?
Potentially, yes.
The US already spends enormous amounts servicing its debt. Reuters reports that interest payments have become one of the largest components of federal spending, while rising rates increase the cost of refinancing existing obligations.
Now add a prolonged military conflict.
Even if the direct cost of the Iran campaign is manageable relative to the size of the US economy, the wider economic effects can become substantial.
Washington could face higher defence expenditure at the same time as slower economic growth and more expensive borrowing.
That is how a military conflict can become a fiscal multiplier.
The Real Threat Is a Long War
A short military campaign would be far easier for the US economy to absorb than a prolonged conflict.
If the Iran war moves toward negotiations, energy markets stabilise and military spending eventually declines, the financial impact could remain manageable.
But if the conflict becomes prolonged, Washington could face a much more complicated environment.
A long war could mean:
Higher defence spending → larger deficits → more Treasury issuance → higher yields → higher interest costs.
At the same time:
Higher oil prices → higher inflation → fewer opportunities for rate cuts → more expensive borrowing.
That combination would put increasing pressure on the US fiscal position.
Why the $40 Trillion Figure Matters Globally
America’s debt is not simply an American problem.
US Treasury securities are deeply embedded in the global financial system.
Banks, pension funds, central banks, insurance companies and investors around the world hold US government debt.
If Treasury yields rise sharply, the consequences can spread across global financial markets.
The US dollar can also come under pressure if investors begin to reassess the country’s fiscal trajectory.
Recent market reactions to the Treasury buyback announcement demonstrate how closely global investors are watching US borrowing conditions. Global bonds and equities recovered after the Treasury announced its intervention, showing how sensitive markets are to changes in US debt-market liquidity.
Europe Will Feel the Consequences Too
The Iran war is also creating a financial problem for Europe.
European governments are simultaneously facing higher energy costs, defence spending pressures and the possibility of prolonged geopolitical instability.
Government bond yields in several major economies have risen alongside US yields as markets reassessed inflation and fiscal risks linked to the conflict.
This means the Iran war could create a broader Western fiscal squeeze.
The United States has the dollar and the world’s deepest Treasury market.
Europe does not have the same degree of financial privilege.
If global borrowing costs remain elevated, European governments could find it harder to finance increased defence expenditure while protecting social programmes and managing energy costs.
China’s Position Could Become More Interesting
A prolonged US fiscal squeeze could also have geopolitical consequences for China.
Beijing has spent years challenging American economic dominance and promoting greater diversification away from the dollar.
China does not need the United States to experience a financial crisis to benefit strategically.
A gradual decline in confidence in US fiscal management could be enough to strengthen arguments for alternative currencies, payment systems and financial arrangements.
However, it would be premature to conclude that the $40 trillion milestone automatically threatens the dollar’s global role.
The US still possesses enormous financial advantages, including the depth and liquidity of its capital markets and the dollar’s central position in international finance.
The real issue is whether those advantages remain strong enough to offset rapidly rising fiscal costs.
The Iran War Could Become a Test of American Economic Power
America has historically demonstrated that military power and financial power reinforce each other.
Washington can deploy military forces globally partly because it has enormous economic capacity.
But the relationship works in reverse as well.
Military commitments consume economic resources.
The Iran war therefore represents a test of whether the United States can maintain global military commitments while simultaneously managing one of the largest debt burdens in its history.
The $40 trillion milestone makes that question impossible to ignore.
Is America Approaching a Debt Crisis?
Not necessarily.
A $40 trillion debt figure by itself does not mean the United States is about to default.
The US government borrows in its own currency, possesses a huge tax base and remains central to the global financial system.
But the risk lies in the trajectory.
The more important questions are:
How quickly is the debt growing?
How expensive is it to service?
How high must interest rates remain?
How much additional borrowing will the Iran war require?
And will investors continue to absorb US debt at acceptable yields?
Those questions matter much more than the headline $40 trillion number alone.
Trump’s Iran Strategy Faces a Financial Constraint
This creates a political challenge for President Donald Trump.
A president can order military operations much faster than Congress can restructure America’s fiscal position.
The administration may be able to expand defence spending to meet immediate strategic requirements, but the financial consequences accumulate over time.
The political problem is particularly complicated because reducing spending, increasing taxes or cutting major entitlement programmes are all politically difficult.
That leaves borrowing as the easiest short-term solution.
But borrowing becomes increasingly expensive when interest rates are high.
This is why the bond market is becoming an important constraint on US foreign policy.
Could Markets Become a Check on War?
This may be the most interesting strategic consequence.
For decades, US presidents have had enormous freedom to use America’s military power overseas.
But a highly indebted America faces another form of power: financial market discipline.
If investors become increasingly concerned about the fiscal consequences of war, Treasury yields could rise.
Higher yields increase government borrowing costs.
That can create pressure on policymakers to reduce spending or seek diplomatic solutions.
The bond market therefore does not need to oppose a war politically to constrain it economically.
The Bigger Risk: Stagflation
The most uncomfortable scenario would be stagflation.
That means:
Higher prices + weaker economic growth + high interest rates.
An extended Iran conflict could increase energy prices while simultaneously damaging consumer and business confidence.
The Federal Reserve would then face an extremely difficult choice.
Cut rates and risk persistent inflation?
Or maintain restrictive policy and risk deeper economic weakness?
Neither option would be attractive.
What Happens If the Iran War Ends Soon?
A diplomatic breakthrough would significantly change the economic picture.
A ceasefire or durable agreement could lower oil-market risk, reduce geopolitical uncertainty and allow investors to reassess the trajectory of inflation and interest rates.
Treasury yields could stabilise without requiring aggressive intervention.
That would give Washington more room to address its underlying fiscal problem.
But even a successful end to the Iran war would not erase America’s $40 trillion debt.
The war may have exposed the problem rather than created it.
The Structural Problem Will Remain After the War
This is perhaps the most important conclusion.
The Iran war is not the reason US debt crossed $40 trillion.
The underlying problem is structural.
The United States has spent years running large deficits, and rising interest costs are making those deficits increasingly difficult to manage.
The war adds pressure to an already stretched system.
The Treasury’s buyback programme can improve liquidity and temporarily calm investors, but the longer-term challenge requires fiscal policy rather than market intervention.
As the Financial Times and other market analysts have emphasised, the Treasury’s intervention addresses market liquidity, not the underlying fiscal imbalance.
The Iran War Is Becoming a Test of America’s Financial Power
The most important story behind the $40 trillion US debt milestone is not the number itself.
It is the timing.
America is reaching this extraordinary debt level while fighting a major war, confronting energy-market instability and facing elevated long-term borrowing costs. At the same time, the Treasury is intervening to stabilise the bond market after long-term yields reached multi-year highs.
That combination creates a new strategic reality.
America remains the world’s dominant military and financial power, but its fiscal room is becoming more constrained.
The Iran war therefore raises a question that goes beyond Tehran and Washington:
How long can the United States sustain an expensive global military strategy when the cost of servicing its own debt is becoming one of the government’s biggest financial burdens?
If the war ends quickly, Washington may have time to address the underlying problem.
If it becomes prolonged, higher defence spending, oil inflation and elevated interest rates could reinforce one another and make America’s fiscal challenge significantly harder.
The $40 trillion milestone should therefore be viewed not as an immediate US debt crisis, but as a warning about the rising economic price of America’s global strategic commitments.
The battlefield may be in the Middle East.
But increasingly, one of the most important fronts of the Iran war is the US Treasury market.
