For three decades after the Cold War, NATO member states no longer faced a major threat, and focussed on out-of-area operations. They took the opportunity to reduce defence spending and foster their own national defence industries; interoperability was limited to air and maritime missions on a small scale. The 2014 Russian annexation of Crimea and war by proxy in eastern Donbass was a wake-up call, while China’s creeping seizure and fortification of islands in the South China Sea, as well as its relentless acquisition of Western technologies, similarly alerted the Western leadership to a less benign strategic environment. But the real shift occurred in 2022. China and Russia not only announced their ‘unlimited friendship’, but made clear their intention to reduce American hegemony by breaking up the NATO alliance and its Pacific equivalents. This volume is the first account of the challenges and solutions for so-called strategic integration in this coercive global situation. The contributors show, thematically and through selected national case-studies, how strategic integration and interoperability are conceived, debated, problematised and resolved. The chapters are written with specific reference to the illegal Russian invasion of Ukraine, which has galvanised a new era of integration and alliance cooperation within NATO.