On September 11, 2001, terrorist attacks on the United States transformed national security, and energy was no exception. Nuclear fuel shipments were halted, major facilities entered heightened alert, and federal agencies accelerated plans to safeguard critical infrastructure. The tragedy exposed vulnerabilities across the energy grid, sparking a new era of resilience, risk management, and cyber-physical security measures. From pipelines to power plants, the focus shifted from efficiency to defense—setting the tone for two decades of energy policy.