Here's what happens when a major military conflict kicks off on a weekend: the markets open for business on Sunday evening looking like they've seen a ghost. U.S. stock futures tumbled and oil prices spiked as President Donald Trump signaled the conflict with Iran could intensify and acknowledged additional American casualties are likely.

Stock Market Futures Slide As Oil Jumps

It was a classic flight-to-safety move, the kind you see when investors suddenly remember the world is a risky place. Dow futures were down about 588 points, or 1.2% to 48,412.00, while S&P 500 and Nasdaq futures each fell more than 1% to 6,812.00 and 24,725.25, respectively.

At the same time, WTI Crude April 26 futures traded 7.3% higher at $71.90 and Gold COMEX April 26 futures were seen 2.55% higher at $5,381.90. When stocks go down, commodities that act as a hedge against chaos—like oil and gold—tend to go up. It's a simple, if grim, equation. The U.S. Dollar Index, which measures the strength of the greenback against a basket of major currencies, rose 0.35% to 97.988, another typical safe-haven move.

The moves followed a major U.S. military operation against Iran that began early Saturday. This wasn't a minor skirmish.

Operation Targets Iranian Military Infrastructure

According to U.S. Central Command, the U.S. launched "Operation Epic Fury" at 1:15 a.m. EST. They deployed a significant arsenal: B-2 stealth bombers, F-16, F-18 and F-22 fighter jets, as well as high mobility artillery rocket systems. In the first 24 hours, U.S. forces struck Iranian command and control centers, air defense systems, ballistic missile sites and naval assets, including ships and submarines. The strikes also targeted facilities linked to the Islamic Revolutionary Guard Corps.

By 9:30 a.m. EST, CENTCOM reported three U.S. service members were killed, five were injured and several others sustained minor injuries. It was the opening salvo in what appears to be a significant escalation.

Trump: ‘There Will Be Likely Be More' Casualties

Trump addressed the nation Sunday afternoon, mourning the fallen troops and delivering a sobering warning that the toll could rise. "We pray for the full recovery of the wounded," Trump said, adding that "sadly, there will be likely be more, before it ends. That's the way it is."

He tried to offer a note of reassurance, saying "[There will] likely be more but we'll do everything possible where that won't be the case," but the message to markets and the public was clear: brace for impact. The conflict is not over, and more pain is expected.

Adding a monumental layer to the geopolitical shock, the joint U.S. and Israeli operation reportedly resulted in the death of Iranian Supreme Leader Ayatollah Ali Khamenei. It's the kind of event that doesn't just move markets for a day; it reshapes the political landscape of a region for years, introducing massive uncertainty about what comes next. And markets, as we saw Sunday night, really don't like uncertainty.