For decades, investors have relied on a simple market correlation. When stock prices fall, government bond prices rise. The premise was the backbone of the classic 60-40 balanced portfolio.

But BlackRock is now warning that this relationship is breaking down—and the reason lies in a mix of geopolitics, energy shocks, and stubborn inflation.

In the latest market note, the world's biggest asset manager has looked into the center of today's market stress – the Strait of Hormuz, a critical chokepoint for global oil and LNG flows. With shipping through the Strait severely disrupted, the world is facing more than just higher prices.

It's a genuine supply shock. Oil has surged back toward $100, and the knock-on effects are spreading through supply chains, raising production costs and feeding inflation.

Since energy touches nearly every part of the economy, this kind of disruption creates a difficult environment. Growth slows while inflation rises.

Why This Time Is Different

BlackRock sees a feedback loop at work. Rising prices increase political and economic pressure, which could eventually limit the conflict, but in the near term, the risk is clear.

That's when bonds are supposed to provide protection. This time, they aren't.

"There are few places to hide from this near-term supply shock in our view. Government bonds and gold are not providing ballast as equities fall. That's because – as we've long said – investors are demanding more compensation for the risk of holding long-term bonds given persistent inflation and high debt levels," their strategists wrote.

The reason is structural. When inflation expectations rise, bond yields have to rise as well to compensate investors. That pushes bond prices down, even as equities are falling. Instead of offsetting risk, bonds begin moving in the same direction.

The market has already seen how disruptive that scenario can be. In April last year, during a tariff-driven shock, both equities and Treasuries sold off simultaneously. The 10-year yield jumped from 4.20% to 4.50% in just four days, marking the sharpest move since 2008. What was supposed to be a safe haven turned into another source of volatility.

BlackRock sees the current environment as a continuation of that pattern, now intensified by an energy-driven inflation shock. With oil pushing prices higher and supply chains under strain, yields are rising again just as risk assets struggle. That situation leaves investors with fewer traditional places to hide.

Plan B Diversification

In response, BlackRock is shifting its preferences. The firm continues to favor U.S. and Japanese equities, while seeing opportunity in emerging-market hard-currency debt – particularly commodity-linked currencies that benefit from high energy prices.

On the other hand, they are cautious on long-duration government bonds, being underweight long U.S. treasuries and particularly Japanese government bonds. In their eyes, even gold is not a reliable long-term hedge at the moment, but more of a tactical tool.

All of the above points to what BlackRock calls a "Plan B" approach to diversification. If bonds no longer provide consistent protection, portfolios need to rely more on assets tied to real economic strength and structural trends. 

It doesn't mean diversification is obsolete, but it does mean adapting to a world of persistent inflation and supply shocks.

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