During my time at the command, the global security environment has become more complex, dynamic, and volatile—perhaps more so than any time in our history. The continued propagation of asymmetric methods, unprecedented proliferation of advancing technologies, and increasingly provocative and destabilizing behavior by current and potential adversaries are making threats today transregional, multidomain, and multifunctional. Some nations are investing in long-term military modernization programs, including capabilities that could pose an existential threat to the United States. A number of others are developing, sustaining, or modernizing their nuclear forces, including weapons and platforms that are mobile, hardened, and underground.