Historically, US earnings outgrew the world by 1%. Post-GFC, this widened to 3%. Investors have extrapolated this recent, higher rate as the new normal, pushing the US CAPE ratio to nearly double that of non-US markets. This represents a historically extreme valuation based on a potentially temporary growth advantage.

Warren Buffett's market indicator, comparing total stock market valuation to GDP, is now over 200%. This far exceeds the 150% peak during the dot-com bubble, suggesting the entire market is in historically overvalued territory. This amplifies the systemic risk of a potential AI-led correction.

A key behavioral indicator of an overheated market is when investors justify buying stocks with indirect, "bank shot" reasoning, like pitching airlines as a play on weight-loss drugs reducing fuel costs. This stretched narrative suggests prices are detaching from fundamentals.

In 2025, US stocks underperformed global peers despite superior earnings growth. Non-US markets saw significant price increases on flat or negative earnings, a divergence that Goldman Sachs Wealth Management believes is unsustainable, reinforcing their long-term US overweight thesis based on earnings fundamentals.

Current market multiples appear rich compared to history, but this view may be shortsighted. The long-term earnings potential unleashed by AI, combined with a higher-quality market composition, could make today's valuations seem artificially high ahead of a major earnings inflection.

While US equities have traditionally been a bellwether for global sentiment, a significant rotation is underway. Stagnant US tech stocks are being overshadowed by strong performance elsewhere, with European equities up 6% and Emerging Market equities up 13%. This suggests capital is flowing into other markets, reducing EM's dependence on US performance.

The S&P's gains are overwhelmingly driven by a handful of AI stocks. This concentration has created a bifurcated market where other sectors, like consumer staples, are being ignored and trade at valuations reminiscent of the 2008 financial crisis. This presents a challenging environment for investors not participating in the AI hype.

While the S&P 500's 19% gain since last year seems strong, it significantly lags global performance. An ETF tracking worldwide stock markets is up 42% in the same period, with markets like South Korea and the Eurozone showing even larger returns. This indicates a potential "sell America" trend among global investors.

The global stock market rally is largely an extension of the U.S. AI story. International markets are benefiting from demand for AI-related inputs (e.g., minerals from Latin America) and as global investors seek to diversify away from highly-valued U.S. tech stocks into other, relatively cheaper markets.