For more than a decade, the playbook for global investors was almost boring in its simplicity: buy U.S. equities and don't look back.

From 2011 through early 2025, the SPDR S&P 500 ETF Trust (NYSE:SPY) outperformed the iShares MSCI All-Country ex U.S. ETF (NYSE:ACWX) by more than 300 percentage points.

International diversification wasn't just unnecessary, it was a drag.

But something shifted in early 2025.

The trade that held firm for nearly 14 years didn't just fade. It cracked.

Since the start of 2025, U.S. equities have underperformed global ex-U.S. stocks by roughly 25 percentage points. ACWX has surged about 40%, while SPY is up just 15%.

According to data from Countryetftracker.com, the ratio between SPY ETF and ACWX ETF has now fallen to levels last seen more than two years ago.

That's not a mild rotation. That could be the onset a regime shift. And technically, the move is even more striking.