AI Concentration and Volatility Shake Global Stock Markets
Global markets face instability as AI-driven corporate concentration triggers volatility in Asia and prompts liquidity interventions by the U.S. Treasury.
Global stock indices are increasingly dominated by a small number of artificial intelligence giants, creating a divergence between benchmarks and broader equity realities. In the United States, Nvidia accounts for 8% of the S&P 500, while concentration is more extreme in Asia, with TSMC representing over 40% of Taiwan's TAIEX. This imbalance has fueled extreme volatility in South Korea, where the KOSPI index surged to record highs in mid-June before plunging 35 percent, leading the Korea Exchange to suspend trading five times in the first half of 2026.
Indicators such as the Shiller price-to-earnings ratio suggest markets are overheating to levels seen during the 2000 dotcom bubble. Beyond equities, the U.S. Treasury Department announced on August 19 that it would at least double its planned purchases of longer-term Treasurys from September 9 through November 4. The agency stated the move is intended "to provide greater liquidity support in longer-dated nominal sectors where there is consistent strong sponsorship from market participants."
While the Treasury's buybacks provided modest support to U.S. markets, analysts remain divided. Some observers characterize the intervention as stealth quantitative easing, while others argue it is a limited recycling operation that cannot expand the monetary base like the Federal Reserve. Additional systemic pressures include a warning from the Reserve Bank of Australia that AI data center construction is straining national capacity and fueling inflation, alongside looming risks of a housing market rollover and an economic crisis in China.
