For a long time, the bond market represented, in the minds of investors, the point of equilibrium. Not necessarily the source of the highest return, but the most predictable one. The place to seek refuge when uncertainty increased — the component that, within a portfolio, was tasked with dampening volatility.

It is no coincidence that government bonds — US Treasuries in particular — were for years described as “risk-free”. A simplification, certainly, but a useful one: it conveyed the idea that a stable reference existed, a foundation upon which everything else could be built.

Today, that perception is changing. Not because government bonds have suddenly become “risky” in the traditional sense, but because the context in which they operate is profoundly different. And with it, the role they play.

When the “risk-free” asset stops providing stability

The turning point was not a single event, but a gradual process. For more than a decade, the financial system benefited from extremely low interest rates and accommodative monetary policy. In that environment, bonds functioned almost intuitively: they offered yield whilst simultaneously tending to rise when equity markets fell.

That relationship — which many took for granted — has progressively weakened.

Today, government bond yields sit at higher levels and, above all, more volatile ones. At certain moments, the market prices in scenarios where yields move above the implicit expectations embedded in central bank decisions. This is not a technical anomaly, but a precise signal: the market is demanding a higher premium to hold even what, until recently, was considered the safest benchmark.

When yields rise, prices fall. It is a simple relationship, but its implications are anything but straightforward. Because what is moving is not a marginal segment of the market, but its very foundation.

The invisible role of bonds: collateral

To truly grasp the scale of this shift, one must look beyond the traditional portfolio perspective.

Bonds — government bonds in particular — are not merely investment instruments. They are the collateral underpinning much of the financial architecture. They are used as security in transactions between institutions, in financing arrangements, in leveraged mechanisms, and in the portfolios of large market participants.

In other words, they are not just an asset. They are infrastructure.

When their value is stable, the system operates smoothly. Transactions proceed without friction, guarantees are sufficient, and credit flows. But when their value begins to fall — even gradually — the effect propagates outward.

Because collateral that loses value is collateral that must be topped up.

The critical transition: from loss of value to demand for liquidity

It is at this juncture that the mechanism becomes most delicate.

If the value of collateral falls, intermediaries require adjustment. This is not a discretionary choice, but an operational necessity. Margins must be maintained; exposures must remain under control.

At that point, whoever has used that collateral is faced with a choice: either provide additional liquidity or reduce their exposure.

In theory, this is an orderly process. In practice, it can become considerably more complex.

Because liquidity — particularly in moments of stress — is not always immediately available. And when it is not, the only alternative is to sell.

Not necessarily what one would choose to sell, but what can most readily be liquidated.

The subtler risk: synchronisation

Up to this point, the mechanism might appear manageable. The problem arises when it affects not a single participant, but many.

When yields rise sharply and broadly, the loss of collateral value is not isolated. It affects a large portion of the system simultaneously. Consequently, calls for margin top-ups multiply at the very same moment.

This is where an often-underestimated factor comes into play: synchronisation.

Many participants, at the same instant, find themselves having to source liquidity. And they do so in a context where liquidity is more costly, more selective, and less abundant than it has been in the recent past.

The result is generalised downward pressure on asset prices. Not because those assets have suddenly become less sound, but because they must be sold.

The link to the margin call

This process is closely connected to the margin call phenomenon. When collateral value falls, margin requirements increase. When those requirements cannot be met with immediate liquidity, forced selling is triggered.

These sales contribute to pushing prices lower still, feeding a cycle that can become self-reinforcing.

This is not a new mechanism. But in an environment where the bond market is more volatile and interest rates are higher, it tends to manifest with greater frequency and intensity.

And it is here that the subject ceases to be merely technical and becomes systemic.

Why this changes the role of bonds

All of this leads to a consideration that, until a few years ago, would have seemed counterintuitive.

Bonds have not lost their function. They remain fundamental instruments for portfolio construction. But the way in which they fulfil that function has changed.

Under certain conditions, they no longer act as an immediate stabilising element. On the contrary, they can become the origin from which tensions propagate.

Not because they are inherently fragile, but because they are central. And when something central moves, that movement transmits itself.

In this sense, the bond market may take on a different role: no longer purely defensive, but also potentially amplifying.

What this means for the investor

For those who invest, this does not imply abandoning bonds or calling their role into question. That would be a superficial reading.

It implies, rather, a shift in perspective.

It means recognising that:

  • the defensive function of bonds is not automatic
  • the interest rate environment is a determining factor
  • stability depends on equilibria that are more complex than in the recent past

And above all, it means understanding that risk does not reside solely in the most conspicuous instruments, but also in those that form the foundation of the system.

Conclusion

The concept of “risk-free” has not disappeared, but it has lost some of its immediate operational relevance. It no longer represents a guarantee of short-term stability, but a theoretical reference that can pass through phases of stress.

When government bonds — the heart of the financial system — come under pressure, the signal is never marginal. It is, on the contrary, an indication that concerns the entire balance of markets.

And this is perhaps the most important point to grasp:

the bond market is no longer solely that which protects.

In certain phases, it is that which reveals — and sometimes amplifies — the fragilities of the system.