An American war against China or Russia would be truly awful. Even if the United States won — no sure thing — it could well suffer costs and casualties that would make the toll of the Iraq and Afghanistan wars seem minor by comparison. So is there a way the U.S. could stymie a Chinese attack in the Pacific, or a Russian land-grab in Eastern Europe, without having to defeat enemy forces head-on? This is the motivating question behind the idea of "horizontal escalation."
Horizontal escalation is a strategic concept that relies on attacking an adversary's weaknesses outside the theater where the fighting started, so as to avoid confronting its strengths within that theater. It is an alluring idea that has won support from some key national security professionals. Unfortunately, it probably won't work.
Horizontal escalation is a response to a genuinely difficult problem: the immense challenges associated with directly defeating Chinese or Russian aggression.