Integrating effectively has always provided a strategic edge, from the ancient world to the present day. Integration is a central theme of the 2022 National Defense Strategy. Here we ask: Why is the United States seeking to integrate now—and how can it integrate better? Now, for the first time since winning the Cold War, the United States must respond to a competitor strong across all levers of power—and so if it wants to compete it must integrate for the character of our new era of competition. This report traces integration as a strategic edge from the 1500s to the present, to identify key themes for the success (or failure) of US integration in the 2020s and 2030s. Three overarching sets of issues emerge: integration militarily; integration across multiple sources of power; and civil-military integration within the state. Integrating with allies and integrating technology will also be key for the United States. All are complex, so to help make them more tractable for practitioners we introduce simple concepts to deal with complex environments (e.g. the “adjacent possible”). We also introduce a powerful new field of cognitive science (metacognition or “thinking about thinking”) that can give the United States an edge for developing the humans, and human-machine teams, that will always lie at the heart of integrated US power.