President Donald Trump announced that the U.S. will share nuclear-powered submarine technology with South Korea, marking a landmark change in military cooperation. He also directed the American military to resume nuclear weapons testing after a 33-year hiatus. These moves signal a sharp pivot in U.S. defense strategy, aiming to strengthen alliances and respond to rival powers’ growing capabilities. The submarine deal opens the door to deeper South Korean-U.S. collaboration, while the testing order challenges long-standing arms control norms.