In his recent study of U.S.-China relations, Harvard professor Graham Allison provocatively asks whether the two superpowers of the 21st century are destined for war. After studying similar situations over the past 2,500 years -- when a rising power challenges an existing power -- the answer is that, more often than not, war is likely. The U.S. and China certainly have a basket of troublesome issues over which they disagree -- trade imbalances, collisions in cyberspace, Chinese territorial claims in the South China Sea, North Korea and uneasy Sino-Japanese relations.

The good news is that in this turbulent period, the international system has more effective tools to deal with conflict between states than ever before. Communications are instantaneous, there are international organizations and forums in which problems can be aired, economies are highly intertwined, and there is a plethora of mechanisms (academic conferences, business engagements, social networks) for informal dialog. But the possibility of a military confrontation between a rising China -- more nationalistic and muscular under President Xi Jinping -- and the U.S., led by an unpredictable and inexperienced president, cannot be ignored.

What does the balance of military power tell us about a potential war? What are the differences in the combat capability of the two nations? What would a conflict look like?

First, it is important to understand the differing defense aspirations of the two nations. The U.S. has a truly global set of security commitments enshrined in treaties and less formal arrangements. These include formal pacts with 28 NATO nations, Japan, South Korea, Australia and many others; as well as highly developed military relationships with Israel, Jordan, Singapore, Sweden, Finland and Afghanistan to name but a few.

China, on the other hand, has few formal alliances and does not -- at least at the moment -- aspire to operate a truly global security network. While Xi is beginning to talk about a more global military presence (and has opened China's first overseas military base on the highly strategic Horn of Africa), this difference in ambition will persist into the next decade and probably beyond. At present, China seeks the ability to control East Asia, dominate the South China Sea, operate at will in the East China Sea, overpower any Asian competitor (notably Japan), and compete with the U.S. in the region.

Even though the U.S. defense budget of around $600 billion dwarfs China's estimated spending of perhaps $200 billion (exact figures are hard to obtain, although Beijing certainly has the second largest military budget in the world), the military balance is approximately equal in East Asia. China's $200 billion focused on regional security roughly equals the U.S. spending and presence in the Pacific. Importantly, Chinese military spending and operations are increasing, while the U.S.'s are largely static.

Narrowing advantage

A second key point of comparison is the capability of naval and air forces. There is virtually no scenario in which large numbers of U.S. ground troops would fight Chinese ground troops (numbering 1.6 million, the largest army in the world), with the possible exception of a repeat of the Chinese and U.S. intervention on the Korean Peninsula in the 1950s on opposite sides -- and that is hard to imagine. Therefore, the balance between the two countries in naval and air forces -- where the chances of conflict are far higher -- is vital to understand.

Here the U.S. enjoys a narrow but dwindling technology advantage. U.S. advanced jet fighters (both carrier and land-based) are still about a generation ahead of their Chinese counterparts. Pilot proficiency is also higher, and the ability to operate from massive aircraft carriers (which can travel nearly 1,000 miles daily, are hard to target precisely, and carry 80 combat aircraft) is an advantage. On the other hand, Chinese hypersonic missiles, satellite targeting, and quiet diesel submarines can threaten U.S. warships within 800 or so miles of the Chinese coast. As China's technology and defense spending increase over the coming years, this narrow U.S. advantage in maritime and air forces will reduce further.

Thirdly, the balance of strategic nuclear forces is worth examining; and here the U.S. enjoys its largest advantage over China. The U.S. operates a continuous, highly capable force of nuclear-armed ballistic missile submarines at sea, which China cannot. The U.S. has a powerful long range, land-based air force with the ability to deliver nuclear weapons; this is a lacuna in the Chinese inventory. Both nations have intercontinental ballistic missiles in land silos, although China has far fewer. While the U.S. has the advantage here, there is a very low likelihood of using strategic nuclear weapons, making this less significant than the two other factors.

Finally, there is the balance in the newest venue of potential conflict: cyberspace. Here the two nations have a roughly equal level of capability in offensive cyber tools. The Chinese have shown the ability to blend commercial, military and political objectives seamlessly in cyberspace, and are more advanced than the U.S. in developing a dedicated cyber force. Their PLA Cyber Unit 61398 is well-known for its military operations -- which led the U.S. to indict five officers in 2014 for their attacks on private U.S. companies.

Overall, the U.S. and China in the military sphere are rather like an eagle and a dragon -- formidable in nature, different in ambition and bringing powerful but distinct tools to battle. The balance between them is difficult to define precisely, but within the East Asia region is on rough parity. Above all, we need to apply all the tools of diplomacy to ensure the two superpowers do not end up in a fight that would be to neither's advantage.

James Stavridis, a retired four-star U.S. Navy admiral, was the 16th supreme allied commander at NATO and spent over half of his career in the Pacific Fleet. He is dean of The Fletcher School of Law and Diplomacy at Tufts University.