The Bond Buyer of Last Resort

A history of debt monetization and the three tiers of sovereign borrowers

May 15, 2026

Every government, eventually, faces the same question. What happens when the bills come due and the bond auction is light? When the deficit keeps growing but the buyers grow tired? When the supply of new debt outruns the private appetite to absorb it?

The honest answer is that it depends entirely on what kind of borrower you are. A family that needs to refinance its mortgage at a higher rate has options. A family that has run its credit cards up to the limit, denominated in a currency it cannot print, has very few. The same logic governs sovereigns. There is a hierarchy of borrowers, and where you sit in that hierarchy determines almost everything about how much room you have, how fast it runs out, and what happens when it does.

I want to walk through that hierarchy today, because I think it is the single most important framework for understanding what is happening in global bond markets right now. There are three tiers, and the rules are different in each one. Reserve currency issuers have the longest leash. Countries that borrow in their own currency without reserve status have a shorter leash. Countries that borrow in someone else's currency have almost no leash at all. History gives us clean examples of each, and the lessons travel.

Debt monetization is what happens when the central bank steps in to buy the government's debt that private investors will not absorb at prevailing prices. The mechanic is simple. The Treasury issues bonds. Private buyers --- pension funds, banks, foreign central banks, insurance companies, individual savers --- bid for them. If their bids do not clear the supply at a yield the government considers acceptable, somebody has to fill the gap. The central bank, with the legal authority to create currency, becomes the buyer of last resort. Bonds go onto the central bank's balance sheet, and new money is created in the process.

The label "monetization" carries a stigma it does not always deserve. Sometimes a central bank buys government bonds for legitimate monetary-policy reasons --- to push down long-term interest rates when the economy is weak, or to provide liquidity during a panic. Other times it buys because the fiscal authority has run out of willing private lenders and has, in effect, asked the central bank to print the difference. The line between the two can be blurry in real time. What matters is the consequence. When a central bank absorbs government debt at scale, it expands the money supply against a backdrop of unchanged real output, and over time that pressure leaks into prices, the currency, or both.

The question my clients ask me is simpler than the textbook version. How high will rates rise before someone intervenes? The answer changes dramatically depending on which tier of borrower we are talking about.

The most painful tier is also the simplest to describe. When a country borrows in a currency it cannot print --- typically the U.S. dollar, sometimes the euro --- it has surrendered the option to monetize. There is no bond buyer of last resort, because the central bank cannot create dollars. When demand for the debt falls short of supply, the choice is brutal: pay whatever rate the market demands, find an outside lender like the IMF, or default.

The 1980s Latin American debt crisis is the textbook case. When Paul Volcker raised the U.S. federal funds rate sharply to break domestic inflation, dollar borrowing costs spiked worldwide. Mexico had roughly $43 billion in external debt, much of it owed to U.S. and Japanese banks, and in August 1982 it announced it could not meet its obligations.¹ The default cascaded across the region. Brazil, Argentina, Chile, Venezuela --- one after another, the dollar-denominated obligations became unpayable. None of these countries could "just print money" to solve the problem, because their problem was not denominated in money they could print.

Argentina is the recurring cautionary tale. By the time of its 2001 collapse, more than half of Argentine government debt was issued in dollars.² When confidence broke, depositors pulled roughly $18 billion --- about 20 percent of bank deposits --- out of the system over the course of 2001.³ The peso peg to the dollar broke. The government defaulted on the bulk of its foreign-currency obligations, and by mid-2002 the public-debt-to-GDP ratio had reached roughly 119 percent.³ There was no domestic central-bank rescue available, because the rescue would have required dollars the central bank did not have.

The pattern repeats across emerging markets. Turkey's experience over the last several years is the more recent variant. Annual consumer inflation in Turkey ran multi-year highs in 2022 after the central bank cut policy rates against the recommendation of conventional economic doctrine, and the lira came under sustained pressure that required large foreign-exchange intervention and the introduction of an FX-protected deposit scheme to stabilize.⁴ The takeaway is the same one Argentine pensioners learned in 2001. If you cannot print the currency your debt is denominated in, the market gets to set the price, and the price can be ruinous. Figure 1 illustrates the basic problem these countries face.

The intervention threshold in this tier is functionally infinite, because there is no domestic intervention available. Either the IMF steps in with a program, or rates rise until the country defaults. There is no soft landing.

Figure 1: Foreign-currency share of government debt at moments of stress. Sources: St. Louis Fed (2021); IMF.

Countries that borrow in their own currency, but lack reserve currency status, have a real but limited safety net. They can monetize. The question is at what cost. History suggests the answer is "considerable, but bearable, until it isn't."

The United Kingdom's experience in September 2022 is the cleanest modern example. The new government announced a so-called "mini-budget" on September 23, 2022, containing roughly £45 billion in unfunded tax cuts.⁵ The bond market's reaction was immediate. The 30-year gilt yield jumped roughly 140 basis points in the days that followed, triggering a forced-selling spiral among UK pension funds running liability-driven investment strategies.⁶ The Bank of England intervened on September 28, announcing a temporary program of long-dated gilt purchases. Between September 28 and October 14, the BoE purchased £19.3 billion of gilts --- £12.1 billion of conventional gilts and £7.2 billion of index-linked.⁷ Those gilts were later sold back to the market in an orderly fashion between November 29, 2022 and January 12, 2023.

Figure 2 shows the magnitude of the move and the speed of the intervention. The lesson is instructive. The UK is not a reserve currency issuer in the way the United States is, but it borrows in its own currency, which means the Bank of England retains the legal authority to step in. It did step in --- but the trigger was financial stability, not yield level alone. A 140-basis-point move in long-dated yields would have been considered painful but not catastrophic in earlier decades. What forced intervention was not the rate itself, but the cascade of forced selling threatening to take down pension funds.

Japan offers a more deliberate version of the same lesson. From September 2016 through March 2024, the Bank of Japan operated under an explicit framework called "Yield Curve Control."⁸ Short-term rates were pinned at minus 0.1 percent, and the 10-year Japanese government bond yield was targeted at "around zero percent." When pressure built, the BoJ widened the tolerance band. In December 2022, it expanded the allowed range to plus or minus 0.5 percent. In July 2023, the upper reference point was lifted to 1.0 percent.⁹ Each adjustment was a recognition that the original cap was no longer holding without massive central-bank purchases. By March 2024, the BoJ formally ended YCC and raised its policy rate.

Figure 3 traces the path. The Japanese experience is the textbook case of a tier-two country exercising its monetization option to the fullest. The Bank of Japan came to own a remarkable share of its own government's debt --- a sustained, structural intervention that lasted nearly eight years. The cost was a meaningfully weaker yen and persistent questions about an eventual exit, but Japan never experienced a true funding crisis. Borrowing in your own currency, even without reserve status, gives you that.

The European sovereign-debt crisis of 2010 through 2012 is the awkward middle case. Individual euro-area countries --- Italy, Spain, Greece, Portugal, Ireland --- had given up the ability to print their own currency when they joined the euro. They had effectively become tier-one borrowers within a tier-two currency block. By July 2012, Italian 10-year yields exceeded 7 percent and Spanish 10-year spreads versus Germany had reached 6 percentage points; Greek, Portuguese, and Irish spreads were wider still.¹⁰ The crisis broke on July 26, 2012, when European Central Bank President Mario Draghi declared in London that the ECB was prepared to do "whatever it takes" to preserve the euro.¹¹ The Outright Monetary Transactions program was formally announced on August 2 and detailed on September 6, 2012.¹²

The OMT program was never actually used. The mere commitment was enough. Within months of the announcement, long-term sovereign spreads versus Germany fell roughly 350 to 450 basis points for Spain, Italy, and Ireland, and more than 600 basis points for Portugal.¹³ Figure 4 shows the timeline. The lesson is striking. Credible monetization power, even unused, is worth several percentage points of yield. The threshold for ECB action turned out to be roughly the point at which the survival of the currency union itself came into question --- a much higher bar than the BoE faced in 2022, but a real and quantifiable one.

Figure 2: UK 30-year gilt yield through the September 2022 LDI crisis. Source: Bank of England.

Figure 3: Bank of Japan Yield Curve Control regime (2016-2024). Source: Bank of Japan policy releases.

Figure 4: Italian and Spanish 10-year yields through the OMT announcement. Source: ECB working papers.

The United States sits in a category of its own. The dollar is the world's reserve currency, which means foreign central banks, foreign commercial banks, multinational corporations, and global savers all hold dollar assets as their default. That structural demand for dollars translates into structural demand for U.S. Treasury debt. The leash is longer, and when intervention does come, the costs are partially exported to the rest of the world rather than absorbed entirely at home.

The cleanest historical example of explicit U.S. debt monetization comes from World War II and its aftermath. From April 1942 through March 1951, the Federal Reserve pegged Treasury bill yields at 0.375 percent and capped long-term Treasury bond yields at 2.5 percent.¹⁴ The Fed bought whatever quantity of Treasuries was needed to hold those yields, regardless of inflation, regardless of the size of the deficit, regardless of what the market would have demanded in the absence of the cap. It was textbook monetization, undertaken to finance the war effort and to allow the Treasury to roll over the wartime debt at affordable rates.

The arrangement worked, in the narrow sense that the Treasury never faced a failed auction. But the cost was real. By the second half of 1950, consumer prices were rising at a 7.7 percent annual rate, and in the first quarter of 1951 the rate accelerated to 17.2 percent.¹⁵ The Fed wanted to fight the inflation by raising rates; the Treasury wanted the peg to continue. The dispute ended on March 4, 1951, with the Treasury-Federal Reserve Accord, which restored the Federal Reserve's independence to set monetary policy without regard to the cost of financing the federal debt.¹⁶ At the time of the accord, the long-term bond rate was 2.47 percent, just below the cap. Figure 5 shows the period.

The modern reserve-currency playbook looks different on the surface but rhymes underneath. The Federal Reserve's quantitative easing programs from 2008 through 2014, and again in 2020 through 2022, were never described as debt monetization. They were framed as monetary-policy tools intended to push down long-term rates when the policy rate had hit zero. But the mechanic was identical to 1942 --- the central bank bought enormous quantities of Treasury debt, expanded its balance sheet, and in doing so absorbed supply that the private market might otherwise have demanded a higher yield to absorb. The 2020 episode in particular saw the Fed step in within days of a Treasury market dislocation in mid-March 2020, well before yields rose meaningfully. The intervention threshold for a reserve currency issuer is essentially "whenever the central bank feels the market is becoming disorderly," not a specific yield level.

What is the upper bound on how high yields can go before the Fed feels compelled to act? History does not give us a clean number. The 10-year Treasury yield reached 15.68 percent on October 2, 1981, without any monetization response --- but that was a deliberate Fed-driven episode under Volcker, designed to crush inflation.¹⁷ The 10-year yield climbed above 5 percent on October 19, 2023, peaking near 5.05 percent, with no formal intervention.¹⁸ The reserve-currency leash is long enough that we have not, in the modern era, seen the Fed forced to cap yields the way the BoE was in 2022 or the BoJ was for nearly a decade. Whether that leash extends indefinitely is, in my view, the most important question in macro markets today.

Figure 5: U.S. long-term Treasury yield under the wartime peg (1940-1955). Sources: FRASER, NY Fed.

Pulling the three tiers together, the pattern is clear. Foreign-currency borrowers have no domestic intervention option at all; rates rise until the country pays, defaults, or accepts an IMF program. Own-currency borrowers can and do intervene, but the trigger is usually financial-system disorder rather than a specific yield level --- the UK acted within days of a 140-basis-point move in long-dated yields, Japan acted whenever its YCC band was tested, and the ECB acted only after 10-year peripheral yields had crossed roughly 7 percent and the currency union itself was visibly under threat. Reserve-currency issuers have the longest leash and the most flexibility in how they intervene, but the historical record shows they will intervene when they choose to, not at a predictable rate level.

The other lesson is about cost. Tier-one countries pay in default and recession. Tier-two countries pay primarily in currency weakness --- the yen depreciated meaningfully against the dollar during the YCC period, and the pound dropped sharply during the 2022 gilt episode before recovering. Tier-three reserve issuers pay too, but the cost is more diffuse and shows up in inflation, in the value of the currency over longer horizons, and in the willingness of foreign holders to keep accumulating the debt at all. The U.S. spent the late 1940s and early 1950s monetizing wartime debt and emerged with significant inflation but with the financial system intact and the dollar still credible. That is the privilege of reserve status.

The hardest cases in history are the ones where reserve status erodes during a monetization episode. Sterling held reserve status into the 1950s and 1960s before gradually losing it. Weimar Germany is the extreme version --- a country that, on paper, was a tier-two own-currency borrower, but whose central bank accommodated such large deficits through discounting government securities that the currency collapsed entirely. By November 1923, German prices were rising at roughly 20.9 percent per day before the stabilization.¹⁹ The Reichsbank had the legal authority to monetize. The market simply stopped accepting the currency it was monetizing in. That is the outer bound of what tier-two privilege can buy you when fiscal discipline disappears.

The reason this history matters to us, as American investors holding dollar assets, is that the United States is the test case for how long a reserve-currency issuer's leash actually is. Federal debt held by the public has grown enormously over the last two decades. Foreign holdings as a share of marketable Treasury debt have declined from their post-financial-crisis peak. The Fed has been allowing its balance sheet to shrink, which means the buyer-of-last-resort presence in the market is smaller than it was a few years ago. None of these facts mean a debt monetization episode is imminent. They mean the question is more live than it has been in a generation.

The strategic implications for portfolios are not radical, but they are real. First, duration matters. If we accept that the U.S. retains a long leash but that the leash is not infinite, then very long-duration nominal Treasury exposure carries more tail risk than it did during the disinflationary period from 1980 through 2020. Second, real assets matter. In every historical episode of debt monetization, the assets that protected purchasing power were those tied to physical scarcity --- productive land, hard commodities, productive companies with pricing power, and to varying degrees gold. Third, currency diversification matters more than it has in decades. The dollar's reserve status is a remarkable asset, but it is an asset whose value depends on how much of it gets created and how trusted the issuer remains.

The Perissos approach to portfolio management is built for exactly this kind of regime uncertainty. Rather than committing to a static allocation that depends on a single forecast about how the monetization question resolves, we use real-time signal-driven inputs --- regime detection, dynamic beta targeting, optimization across asset classes --- to shift exposure as conditions change. We do not need to know in advance whether the Fed will be forced to intervene at a 6 percent 10-year or whether the long leash holds. We need to be able to respond if and when the signals turn. That is the design.

The discipline I want to leave clients with is this. Debt monetization, in some form, is not a fringe historical event. It is one of the most common tools governments have used when debt growth outruns voluntary demand. The interesting question is never "will it happen" --- it is which tier of borrower you are, what the trigger threshold looks like, and what assets sit on the other side of the intervention.

History does not predict when the next episode comes, but it tells us with reasonable clarity what each tier of borrower can and cannot do when private demand falls short. The United States retains the longest leash that has ever been available to a sovereign borrower. That leash is a privilege, not a guarantee, and the historical record suggests it is best treated as something to respect rather than to lean on.

Our team will continue monitoring the signals that matter most for this question --- Treasury auction dynamics, foreign holdings, Fed balance sheet trajectory, real yields, and the underlying fiscal path. Adaptive Allocation is designed to respond to changes in those signals rather than to predict them. If you would like to discuss how your specific household fits into this framework, please reach out.

All my best,

Brandon VanLandingham, CFA, CMT, CFP

Founder / CIO

1. International Monetary Fund, "The Global Debt Crisis of 1982–83," IMF History Series, October 2001. imf.org/external/pubs/ft/history/2001/ch08.pdf 2. Federal Reserve Bank of St. Louis, "Dollar-Denominated Public Debt in Asia and Latin America," August 2021. stlouisfed.org/on-the-economy/2021/august/dollar-exposure-public-debt-asia-latin-america 3. International Monetary Fund, "Lessons from the Crisis in Argentina," IMF Occasional Paper No. 236, 2004. imf.org/external/pubs/NFT/Op/236/op236.pdf 4. Bank for International Settlements, "Recent economic and financial developments in Turkey," speech by Şahap Kavcıoğlu, July 2023. bis.org/review/r230718p.htm 5. Bank of England, "An anatomy of the 2022 gilt market crisis," Working Paper, 2023. bankofengland.co.uk/working-paper/2023/an-anatomy-of-the-2022-gilt-market-crisis 6. International Monetary Fund, "Liability-Driven Investment (LDI) Crisis: United Kingdom," Selected Issues Paper, 2023. imf.org/-/media/files/publications/selected-issues-papers/2023/english/sipea2023049.pdf 7. Bank of England, "Financial stability buy/sell tools: a gilt market case study," Quarterly Bulletin, 2023. bankofengland.co.uk/quarterly-bulletin/2023/2023/financial-stability-buy-sell-tools-a-gilt-market-case-study 8. Bank of Japan, "New Framework for Strengthening Monetary Easing," September 21, 2016. boj.or.jp/en/mopo/mpmdeci/mpr_2016/k160921a.pdf 9. Bank of Japan, "How have the Bank's guidelines for market operations changed?" boj.or.jp/en/about/education/oshiete/seisaku/b42.htm 10. European Central Bank, "The Euro area sovereign debt crisis," Working Paper No. 1419, February 2012. ecb.europa.eu/pub/pdf/scpwps/ecbwp1419.pdf 11. European Central Bank, "The financial and macroeconomic effects of OMT announcements," Working Paper No. 1707. ecb.europa.eu/pub/pdf/scpwps/ecbwp1707.pdf 12. European Central Bank, "Technical features of Outright Monetary Transactions," press release, September 6, 2012. ecb.europa.eu/press/pr/date/2012/html/pr120906_1.en.html 13. European Central Bank, "Twenty Years of the ECB's monetary policy," speech, June 2019. ecb.europa.eu/press/key/date/2019/html/ecb.sp190618.en.html 14. Federal Reserve Bank of St. Louis, FRASER, "Treasury-Federal Reserve Accord of 1951 Timeline." fraser.stlouisfed.org/timeline/treasury-fed-accord 15. Federal Reserve Bank of Richmond, "The Treasury-Fed Accord: A New Narrative Account," Economic Quarterly, Winter 2001. richmondfed.org/publications/research/economic_quarterly/2001/winter/leachhetzel 16. Federal Reserve Bank of New York, "Managing the Treasury Yield Curve in the 1940s," Staff Report 913. newyorkfed.org/medialibrary/media/research/staff_reports/sr913.pdf 17. Federal Reserve Bank of St. Louis, FRED, "Market Yield on U.S. Treasury Securities at 10-Year Constant Maturity," daily series (DGS10). fred.stlouisfed.org/series/DGS10 18. Federal Reserve Board, "The Treasury Tantrum of 2023," FEDS Notes, September 3, 2024. federalreserve.gov/econres/notes/feds-notes/the-treasury-tantrum-of-2023-20240903.html 19. National Bureau of Economic Research, "Stopping Hyperinflation: Lessons from the German Inflation Experience of the 1920s," Working Paper 1675. nber.org/system/files/working_papers/w1675/w1675.pdf

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