Global Bond Rout and Escalating U.S.-Iran Conflict Drag Stocks Lower on First Day of September

U.S. equities slid Tuesday as a global bond selloff and renewed military escalation between the United States and Iran hammered investor sentiment on the first trading day of September. The S&P 500 fell roughly 0.66%, the Dow Jones Industrial Average dropped 0.43%, and the Nasdaq 100 tumbled 1.30%, with technology and semiconductor shares absorbing the sharpest losses.

The catalyst for the bond market turmoil was a fresh surge in oil prices following strikes on two Saudi oil tanks in the Strait of Hormuz, pushing WTI crude to $92 a barrel. President Trump said the U.S. would retaliate against Iran for its latest strikes, intensifying supply risk fears in a strait that once handled around 20 million barrels per day but now exports an estimated 2 to 9 million barrels daily depending on the source. The 10-year Treasury yield climbed to its highest level since January 2025, feeding fears that the Federal Reserve may be forced to raise interest rates to contain renewed inflation pressures. Japan's benchmark yield simultaneously hit 3%, deepening a global duration shock that pressured equities from London to Frankfurt.

Semiconductors led the equity decline. In pre-market trading, SanDisk dropped 3.24% to $1,566.70 on memory sector supply concerns, Intel fell 2.45% to $89.51, SK Hynix slid 2.06% to $164.58 on expanding Chinese memory capacity worries, Micron fell 2.06% to $958.73, AMD slipped 1.73% to $470.72, and Nvidia declined 1.49% to $220.78. Amazon shares also dipped after a joint FTC and 22-state lawsuit alleged more than $20 billion in ad auction overcharges. Energy names bucked the trend, with Chevron and ExxonMobil posting relative strength as crude advanced.

Amid the selling, Humana formally reaffirmed its full-year 2026 adjusted EPS guidance of at least $9.00 ahead of investor meetings, and Broadcom traded under pressure ahead of its upcoming third-quarter fiscal 2026 earnings release. Dell and Palo Alto Networks were set to report results after the close. Anthropic was separately reported to have signed a $35 billion cloud deal with Lambda. Bitcoin opened September swinging between $77,283 and just above $78,000, its volatility coming after a 25% surge in August that left its market capitalization at $1.57 trillion.

The weak open also carried a seasonal dimension: September has historically been the worst calendar month for the S&P 500 since 1928, averaging a 1.1% decline with positive returns in only 44% of years. Analysts noted, however, that the index entered the month trading roughly 8% above its 200-day moving average, a threshold that has historically tilted monthly returns positive.