Eight percentage points of GDP in five years. This is the explosion of global public debt that the IMF projects by 2031, bringing the total above the symbolic 100% of GDP threshold in 2029 — one year earlier than anticipated. This acceleration reflects the conjunction of three simultaneous shocks: rising geopolitical tensions pushing states to rearm, higher interest rates that increase debt servicing, and demographic aging that grows social spending.
Fiscal room for maneuver is shrinking everywhere. Facing this constraint, the question is no longer whether trade-offs will become brutal, but where they will hit first: pensions, health, defense, or climate investment. Governments must now choose their priorities in a context where every euro spent on education or infrastructure becomes one euro less for defense or renewable energy.
The Essential Points
- Global public debt will cross 100% of GDP in 2029, one year earlier than expected according to the IMF
- Military expenditures add an average of 7 points of debt over three years during armament booms
- The United States already reaches 123% public debt, France 112%, Italy 144%
- The interest charge now represents 3.2% of global GDP compared to 1.8% in 2020
- Green investments require an additional 2,400 billion annually according to the OECD
The United States and Europe Accelerate Global Debt
Advanced economies are pulling global public debt upward. The United States already shows 123% debt relative to GDP in 2026, compared to 107% in 2020. The explosion stems directly from post-Covid stimulus plans, Biden’s infrastructure spending, and especially accelerated rearmament facing rivalry with China. The U.S. military budget jumps from 916 billion in 2024 to 1.2 trillion programmed for 2028.
Europe is not escaping this spiral. France reaches 112% public debt, Germany 71%, Italy 144%. The European defense plan adopted in March 2026 provides for 500 billion euros over five years, equivalent to 7% of the Union’s GDP. These military investments are added to spending already programmed for the energy transition and maintaining social systems facing aging populations.
This dynamic reinforces itself. The more geopolitical tensions escalate, the more states dedicate resources to armament at the expense of other items. Global antitrust catches up with technology giants, yet paradoxically, states spend massively to acquire technologies from these same companies for military purposes.
Interest Charges Erode Public Budgets
The return of inflation has resurrected interest rates. The interest charge on public debts now represents 3.2% of global GDP compared to 1.8% in 2020, according to IMF calculations. For the United States, this represents 900 billion dollars annually, more than the defense budget. For France, the interest charge reaches 52 billion euros in 2026, equivalent to the higher education and research budget.
This mechanism creates a ratchet effect. Each additional percentage point in rates mechanically increases financing needs. Italy devotes 4.8% of its GDP to servicing its debt, or 95 billion euros that finance no productive investment. These considerable sums reduce the fiscal space available for public policies by the same amount.
Japan is an exception with an interest charge limited to 1.1% of its GDP despite debt of 261% of GDP. This anomaly is explained by domestic holdings of 90% of Japanese debt and rates kept artificially low by the Bank of Japan. But this strategy is reaching its limits: resurgent inflation is forcing Tokyo to gradually raise its policy rates.
Social Spending Creates Growing Structural Pressure
Demographic aging generates ineluctable budget pressure. In OECD countries, pension spending represents an average of 8.8% of GDP in 2026 compared to 7.1% in 2010. This increase of 1.7 percentage points accelerates: the OECD projects 11.2% of GDP by 2040. Health spending follows the same trajectory, rising from 7.9% to 9.4% of GDP over the same period.
Germany illustrates this structural challenge. With 22% of its population aged over 65, the country devotes 10.1% of its GDP to public pensions. This proportion will reach 12.8% in 2040 according to official projections, an increase of 2.7 percentage points of GDP. Berlin must simultaneously finance its rearmament, energy transition, and social commitments in a context of declining workforce.
France navigates the same constraint. Pension schemes generate a deficit of 13.5 billion euros in 2026 despite the Macron reform. This structural deficit adds to the financing need for health insurance, or 11 billion euros additional. These 24.5 billion represent the equivalent of the French defense budget.
Climate Investment Enters Competition with Other Priorities
The energy transition requires massive investments at a moment when fiscal space is shrinking. The OECD estimates at 2.4 trillion dollars annually the additional green investment needs by 2030 to meet the Paris Agreement. This sum represents 2.4% of global GDP, equivalent to global military spending.
This competition creates new political tensions. The United States adopted the Inflation Reduction Act for 370 billion dollars over ten years, but Donald Trump promises to redirect these funds toward defense. Europe mobilizes 1 trillion euros through the Green Deal, but must simultaneously finance its industrial and military strategic autonomy.
Global debt reaches 109 trillion but financial innovations open new avenues to mobilize private savings, but public budgets remain indispensable for basic infrastructure and fundamental research. This public-private division becomes a central issue in budget trade-offs.
Emerging Countries Face a Double Constraint
Emerging economies face an additional challenge: financing their development while servicing debts denominated in foreign currencies. The debt of developing countries reaches 98.6 trillion dollars in 2026 according to the Institute of International Finance, a 23% increase since 2020. This progression reflects the explosion of investment needs in infrastructure, education, and health.
Brazil exemplifies this tension. Its public debt reaches 89% of GDP in 2026, fueled by investments in the Amazon, digital infrastructure, and social programs. Brasília must simultaneously modernize its armed forces facing regional instabilities and maintain its conditional transfers benefiting 14 million families. The interest charge absorbs 6.2% of Brazilian GDP, reducing margins for productive investment.
India follows a similar trajectory with public debt of 84% of GDP. New Delhi finances massive investments in transportation, energy, and telecommunications infrastructure while modernizing its military facing China. These investments, necessary for economic catch-up, mechanically fuel public debt.
These emerging countries also suffer from capital flow volatility. When investors turn away from emerging markets toward U.S. assets, financing costs explode. This external vulnerability limits their debt capacity and constrains their budget choices.
Brutal Trade-offs Approach in Europe and the United States
Budget constraints are already transforming political debates. In the United States, the Trump administration prepares cuts to social programs to finance rearmament and promised tax cuts. The Congressional Budget Office projects that mandatory spending (Social Security, Medicare, Medicaid) will absorb 77% of federal revenues in 2030 compared to 71% in 2026. This mechanism leaves little room for discretionary investments.
Germany anticipates its own trade-offs. The Bundestag debates relaxing the constitutional “debt brake” to finance both defense and the energy transition simultaneously. This constitutional revision, unthinkable five years ago, illustrates the pressure even the most fiscally orthodox states face.
In France, the debate already opposes defense and ecology. The 2027 budget provides 4 billion euros additional for the military but cuts climate credits by 2.8 billion. This reallocation reveals the implicit prioritization of priorities: security before environment when resources become scarce.
These structural tensions announce increasingly clear-cut political choices. Voters will have to arbitrate between maintaining purchasing power, quality of public services, national security, and climate ambition. No government will be able for long to promise everything without confronting the reality of budget constraints.
The current trajectory leads toward a point where states will lose the capacity to simultaneously respond to all social demands. This prospect is already transforming election campaigns, where candidates must clarify their priorities rather than multiply promises. The age of public budget abundance is closing, opening that of explicit choices between legitimate but competing objectives.