FORT IRWIN, Calif. — As the general paced the briefing room, he displayed a piece of lethal technology and detailed the death and chaos it has caused in Ukraine. Almost 90 Russian soldiers were slain in a single attack in 2022, explained Army Maj. Gen. Curtis Taylor, when Ukrainian forces dropped U.S.-provided rockets on buildings pulsing with electronic signals. Here in the Mojave Desert, where Taylor oversees simulated war designed to prepare U.S. troops for the real thing, the same behavior abounds, he warned. Taylor held up his cellphone. “This device,” he said, “is going to get our soldiers killed.” The U.S. military is undertaking an expansive revision of its approach to war fighting, having largely abandoned the counterinsurgency playbook that was a hallmark of combat in Iraq and Afghanistan to focus instead on preparing for an even larger conflict with more sophisticated adversaries