A Short History of Sovereign Default
Governments have borrowed for as long as there have been governments, but the composition of that borrowing matters. A disproportionate share of sovereign defaults historically involved foreign-currency debt — borrowing in a currency the sovereign can't print. Local-currency default is available as a policy choice; most governments avoid it because the inflation cost of printing is usually preferable to the reputation cost of defaulting.
Research on the consequences of sovereign default documents a consistent pattern: GDP contraction, rating downgrades, higher subsequent borrowing costs, banking-sector stress, trade retaliation, and often political change. Defaults that coincide with banking crises and currency devaluations are especially costly.
What Sovereign Ratings Actually Measure
Bond rating agencies extended their corporate credit analysis to sovereigns: assess the entity's capacity and willingness to service debt, assign a rating on a discrete scale, monitor, and revise. Coverage has expanded dramatically over recent decades, and ratings are now available for most economies.
The process has known weaknesses:
- Upward bias. Rated issuers pay for ratings, which creates commercial pressure.
- Herd behavior. Agencies tend to move together, often with a lag.
- Regional bias. Methodology choices and inputs can advantage certain geographies over others.
- Sticky ratings. Changes in underlying fundamentals show up in ratings after — sometimes well after — they're visible in market prices.
Default rates in Moody's data rise monotonically as ratings fall, so the signal does work — but the signal moves slowly.
Alternatives: CDS Spreads
Sovereign credit default swap spreads trade continuously, incorporate market views in real time, and can move on any day. They're the cleanest market-based measure of sovereign default risk where the CDS market is liquid.
The trade-off: CDS spreads also reflect technical factors (counterparty flows, regulatory shifts, liquidity premiums) that aren't about fundamental default risk. For a valuation, CDS spreads are generally a better input than ratings for countries with active markets, but need to be read with the technicals in mind.
The US Downgrade
Moody's moved the US sovereign rating from Aaa to Aa1 in 2025, citing rising government debt and persistent political dysfunction. The market reaction was muted for three reasons:
- It wasn't a surprise. S&P and Fitch had already made similar moves years earlier, and the fundamentals had been deteriorating for longer.
- The rating change was small. One notch at the top of the scale is not a step-change in perceived credit quality.
- The US Treasury market is structurally the reserve asset. A single-notch downgrade doesn't change the demand architecture.
For valuation practitioners, the downgrade is mostly a footnote. The risk-free rate used in cost-of-capital calculations can continue to be the Treasury yield, with appropriate discussion of what "risk-free" means when the reference sovereign has been downgraded. Equity risk premiums don't need a structural reset.
What Actually Changes
The longer-term implication is less quantitative than directional. The downgrade is another marker in a slow unwinding of US exceptionalism — the idea that US assets carry no country-risk premium by definition. That unwind has been happening in CDS spreads, in the dollar-weakness pattern, and in capital flow decisions for some time. The rating agencies are catching up to what the markets had already priced.
Bottom Line
Sovereign ratings lag, sovereign CDS spreads lead, and cost-of-capital work should use both with appropriate weighting. The US downgrade's mechanical effect on valuation analysis is near zero; its signaling value about the longer-term direction of reserve-asset credibility is larger.