This article explores an emerging dynamic in the international system: Countries across the world are engaged in simultaneous security cooperation with both China and the United States. China and the United States, however, do not provide the same types of security goods. The United States primarily offers regional security—assistance that improves partners’ capabilities to deter or deny external threats to their territory. China primarily offers regime security—assistance that builds partners’ capabilities to control their territory and populations, and often, to prevent threats to a regime's hold on power. Many countries benefit from both types of assistance, and neither China nor the United States is in a strong position to demand exclusivity from third countries. As a result, a growing number of countries are developing nonexclusive, differentiated security relationships with both great powers. We call this phenomenon “security hybridization” and demonstrate that it is theoretically and empirically distinct from traditional balancing and omnibalancing. We illustrate this dynamic with two case studies—Vietnam and the United Arab Emirates. Each country engages in defense cooperation with the United States and, simultaneously, pursues increasingly robust internal security cooperation with China. Security hybridization distinguishes today's great power competition from Cold War rivalry and will likely shape patterns of domestic and global security in the years ahead.

China is a leader in the global transportation industry, with an especially significant position in ocean ports. A mapping of every ocean port outside of China reveals that Chinese firms own or operate terminal assets in ninety-six ports in fifty-three countries. An original dataset of Chinese firms' overseas port holdings documents the geographic distribution, ownership, and operational characteristics of these ports. What are the international security implications of China's global port expansion? An investigation of Chinese firms' ties to the Party-state reveals multiple mechanisms by which the Chinese leadership may direct the use of commercial port assets for strategic purposes. International port terminals that Chinese firms own and operate already provide dual-use capabilities to the People's Liberation Army during peacetime, establishing logistics and intelligence networks that materially enable China to project power into critical regions worldwide. But this form of networked state power is limited in wartime because it depends on commercial facilities in non-allied states. By providing evidence that overseas bases are not the sole index of global power projection capabilities, findings advance research on the identification and measurement of sources of national power. China's leveraging of PRC firms' transnational commercial port network constitutes an underappreciated but consequential form of state power projection.