The main focus of US national security policy has shifted dramatically since the years of the Obama administration, moving away from nation building and counterinsurgency efforts and toward preparing for traditional state-on-state conflict with powerful peers. The sixth edition of US National Security reflects that change. It also addresses such current issues as the impact of an increasingly partisan political process, sharp divisions in public opinion, the ongoing challenges of homeland security, and developments in cyberspace and other possible domains of future warfare. Retaining the successful structure and approach of the previous editions, the book clearly introduces and explores the full range of actors, processes, and politics involved in maintaining US national security.