The United States discarded its oft-misunderstood “two war” doctrine, intended as a template for providing the means to fight two regional wars simultaneously, late last decade. Designed to deter North Korea from launching a war while the United States was involved in fighting against Iran or Iraq (or vice versa,) the idea helped give form to the Department of Defense’s procurement, logistical and basing strategies in the post–Cold War, when the United States no longer needed to face down the Soviet threat. The United States backed away from the doctrine because of changes in the international system, including the rising power of China and the proliferation of highly effective terrorist networks.
But what if the United States had to fight two wars today, and not against states like North Korea and Iran? What if China and Russia sufficiently coordinated with one another to engage in simultaneous hostilities in the Pacific and in Europe?
Could Beijing and Moscow coordinate a pair of crises that would drive two separate U.S. military responses? Maybe, but probably not. Each country has its own goals, and works on its own timeline. More likely, one of the two would opportunistically take advantage of an existing crisis to further its regional claims. For example, Moscow might well decide to push the Baltic States if the United States became involved in a major skirmish in the South China Sea .
In any case, the war would start on the initiative of either Moscow or Beijing. The United States enjoys the benefits of the status quo in both areas, and generally (at least where great powers are concerned) prefers to use diplomatic and economic means to pursue its political ends. While the U.S. might create the conditions for war, Russia or China would pull the trigger.
On the upside, only some of the requirements for fighting in Europe and the Pacific overlap. As was the case in World War II, the U.S. Army would bear the brunt of defending Europe, while the Navy would concentrate on the Pacific. The U.S. Air Force (USAF) would play a supporting role in both theaters.
Russia lacks the ability to fight NATO in the North Atlantic, and probably has no political interest in trying. This means that while the United States and its NATO allies can allocate some resources to threatening Russia’s maritime space (and providing insurance against a Russian naval sortie,) the U.S. Navy (USN) can concentrate its forces in the Pacific . Depending on the length of the conflict and the degree of warning provided, the United States could transport considerable U.S. Army assets to Europe to assist with any serious fighting.
The bulk of American carriers, submarines and surface vessels would concentrate in the Pacific and the Indian Oceans, fighting directly against China’s A2/AD system and sitting astride China’s maritime transit lanes . Long range aviation, including stealth bombers and similar assets, would operate in both theaters as needed.
The U.S. military would be under strong pressure to deliver decisive victory in at least one theater as quickly as possible. This might push the United States to lean heavily in one direction with air, space and cyber assets, hoping to achieve a strategic and political victory that would allow the remainder of its weight to shift to the other theater. Given the strength of U.S. allies in Europe, the United States might initially focus on the conflict in the Pacific.
U.S. alliance structure in the Pacific differs dramatically from that of Europe. Notwithstanding concern over the commitment of specific U.S. allies in Europe, the United States has no reason to fight Russia apart from maintaining the integrity of the NATO alliance. If the United States fights, then Germany, France, Poland and the United Kingdom will follow. In most conventional scenarios, even the European allies alone would give NATO a tremendous medium term advantage over the Russians; Russia might take parts of the Baltics, but it would suffer heavily under NATO airpower, and likely couldn’t hold stolen territory for long. In this context, the USN and USAF would largely play support and coordinative roles, giving the NATO allies the advantage they needed to soundly defeat the Russians. The U.S. nuclear force would provide insurance against a Russian decision to employ tactical or strategic nuclear weapons.
The United States faces more difficult problems in the Pacific. Japan or India might have an interest in the South China Sea, but this hardly guarantees their participation in a war (or even the degree of benevolence of their neutrality.) The alliance structure of any given conflict would depend on the particulars of that conflict; any of the Philippines, Vietnam, South Korea, Japan or Taiwan could become China’s primary target. The rest, U.S. pressure aside, might well prefer to sit on the sidelines. This would put extra pressure on the United States to establish dominance in the Western Pacific with its own assets.