Ukraine drove this lesson home. There will be no war between the United States and Russia over Ukraine. The United States does not have interests there that justify a war, and neither country is in a position militarily to fight a war. The Americans are not deployed for war, and the Russians are not ready to fight the United States.

But the events in Ukraine point to some realities. First, the power of countries shifts, and the Russians had substantially increased their military capabilities since the 1990s. Second, the divergent interests between the two countries, which seemed to disappear in the 1990s, re-emerged. Third, this episode will cause each side to reconsider its military strategy and capabilities, and future crises might well lead to conventional war, nuclear weapons notwithstanding. Ukraine reminds us that peer-to-peer conflict is not inconceivable, and that a strategy and defense policy built on the assumption has little basis in reality. The human condition did not transform itself because of an interregnum in which the United States could not be challenged; the last two decades are an exception to the rule of global affairs defined by war.

U.S. national strategy must be founded on the control of the sea. The oceans protect the United States from everything but terrorism and nuclear missiles. The greatest challenge to U.S. control of the sea is hostile fleets. The best way to defeat hostile fleets is to prevent them from being built. The best way to do that is to maintain the balance of power in Eurasia. The ideal path for this is to ensure continued tensions within Eurasia so that resources are spent defending against land threats rather than building fleets. Given the inherent tensions in Eurasia, the United States needs to do nothing in most cases. In some cases it must send military or economic aid to one side or both. In other cases, it advises.

U.S. Strategy in Eurasia

The main goal here is to avoid the emergence of a regional hegemon fully secure against land threats and with the economic power to challenge the United States at sea. The U.S. strategy in World War I was to refuse to become involved until it appeared, with the abdication of the czar and increasing German aggression at sea, that the British and French might be defeated or the sea-lanes closed. At that point, the United States intervened to block German hegemony. In World War II, the United States remained out of the war until after the French collapsed and it appeared the Soviet Union would collapse — until it seemed something had to be done. Even then, it was only after Hitler's declaration of war on the United States after the Japanese attack on Pearl Harbor that Congress approved Roosevelt's plan to intervene militarily in continental Europe. And in spite of operations in the Mediterranean, the main U.S. thrust didn't occur until 1944 in Normandy, after the German army had been badly weakened.

In order for this strategy, which the U.S. inherited from the British, to work, the United States needs an effective and relevant alliance structure. The balance-of-power strategy assumes that there are core allies who have an interest in aligning with the United States against regional enemies. When I say effective, I mean allies that are capable of defending themselves to a great extent. Allying with the impotent achieves little. By relevant, I mean allies that are geographically positioned to deal with particularly dangerous hegemons.

If we assume Russians to be dangerous hegemons, then the relevant allies are those on the periphery of Russia. For example, Portugal or Italy adds little weight to the equation. As to effectiveness, the allies must be willing to make major commitments to their own national defense. The American relationship in all alliances is that the outcome of conflicts must matter more to the ally than to the United States.

The point here is that NATO, which was extremely valuable during the Cold War, may not be a relevant or effective instrument in a new confrontation with the Russians. Many of the members are not geographically positioned to help, and many are not militarily effective. They cannot balance the Russians. And since the goal of an effective balance-of-power strategy is the avoidance of war while containing a rising power, the lack of an effective deterrence matters a great deal.

It is not certain by any means that Russia is the main threat to American power. Many would point to China. In my view, China's ability to pose a naval threat to the United States is limited, for the time being, by the geography of the South and East China seas. There are a lot of choke points that can be closed. Moreover, a balance of land-based military power is difficult to imagine. But still, the basic principle I have described holds; countries such as South Korea and Japan, which have a more immediate interest in China than the United States does, are supported by the United States to contain China.

In these and other potential cases, the ultimate problem for the United States is that its engagement in Eurasia is at distance. It takes a great deal of time to deploy a technology-heavy force there, and it must be technology-heavy because U.S. forces are always outnumbered when fighting in Eurasia. The United States must have force multipliers. In many cases, the United States is not choosing the point of intervention, but a potential enemy is creating a circumstance where intervention is necessary. Therefore, it is unknown to planners where a war might be fought, and it is unknown what kind of force they will be up against. The only thing certain is that it will be far away and take a long time to build up a force. During Desert Storm, it took six months to go on the offensive.