In Asia, where the enrichment and empowerment of many states is driving growing rivalries, the greatest question of our time is how these contests will play out. The region's geography gives us an important part of the answer.
Asia is divided into two separate strategic realms by an almost unbroken chain of mountains stretching from the Bosphorus to the South China Sea. South of this mountain chain, a potentially dangerous sense of competition is increasing alongside a hunger for more sophisticated arms.
The countries of Asia's southern tier form a single strategic realm, bound together by the common opportunities and anxieties of societies that look to the ocean for vital commercial flows but are also aware of the threats it can bring.
A maritime orientation is a boon to a society's prosperity; more than 90% of all global trade, measured by weight and volume, or 80% measured by value, is carried on the world's maritime highways.
Before the 2008 financial crisis, global maritime traffic was growing faster than global productivity. This was even more pronounced in Asia. In the decade before the crisis, Asia's maritime trade with Europe increased by an average of 20% per year.
The oceans provide maritime states with options to maximize profits for home-grown goods, as well as access to the full range of goods produced elsewhere -- a huge commercial advantage that landlocked states can only dream of.
But while the ocean is a source of prosperity, it can also be a source of danger. A state's coasts are potential front lines in a conflict -- long front lines that offer multiple avenues of attack, beyond any state's capacities to defend them comprehensively.
This is why the world's oceans host a constant display of military power. Even when not at war, heavily-armed navies are at sea, visiting foreign ports, patrolling trade routes and gathering intelligence. For societies whose vital cities, core infrastructure and main industrial capacities are clustered along their coastlines, the promise and the menace of the sea are inseparable.
New tech, new strategy
Two interlinked trends keep security planners in Asia awake at night.
The first is that maritime weapons systems tend to offer rising powers a much greater potential bang for each buck spent on them than similar investment in land-based capabilities. Submarines and anti-ship missiles, for example, offer smaller countries their best prospects of closing the capability gap with larger powers, particularly as a deterrent to other navies operating close to their coastlines.
The second trend concerns naval strategy. There has been a steady shift among the world's navies from deploying power at sea toward deploying power from the sea. Instead of navies battling other navies, they are increasingly configured to wage war from the ocean onto land, or to provide the means for direct assault from the sea.
In both equipment and doctrine, the navies of the major powers are moving toward expeditionary capabilities -- the capacity to project coercive force from the sea onto the land. This can be in the form of sea-based air power, cruise missiles launched from ships or submarines, or amphibious landing forces.
A third consideration adds fuel to Asia's maritime arms race -- "horizontal escalation," or the option of responding to a rival's provocation in one location by threatening its interests in another. The geography of Asia's southern tier and the deepening dependence of its states on seaborne resources offer considerable scope for such escalation of conflicts.
Given these trends, it is unsurprising that Asia's weapons acquisition statistics show a sustained build-up in southern-tier states' maritime capabilities.
In 2012, the Stockholm International Peace Research Institute reported that the period from 2007 to 2011 saw a 200% higher volume of arms transfers into Southeast Asia than there had been between 2002 and 2006. This volume of imports was the highest since the end of the Vietnam War in 1975.
The hardware bonanza
Asia has become a great arms bazaar, its states making the most of cutthroat competition among weapons producers to procure the most effective weapons systems their money can buy.
Thanks to a cascade of maritime weapons purchases along Asia's southern tier, America's ability to dictate the terms of the sea's use, which it has held since World War II, is crumbling.
The only direct challenge to the U.S. Navy's command of the seas comes from China. Beijing has long been alarmed by the U.S. Navy's ability to sail along its coastlines, and by its intelligence-gathering activities. In response, China has been investing intensively in weapons of sea denial.
At the same time, however, India is pursuing similar weapons systems in the Indian Ocean. Although it is as uncomfortable as Beijing about the ability of rival navies to engage in intelligence gathering close to its coasts, under the cloak of freedom of navigation, New Delhi is more strongly motivated by China's growing naval capabilities.
While the two Asian giants continue to square off over their land borders, Indian strategists believe Beijing is preparing to project power into the Indian Ocean once it has dealt with U.S. power in the Pacific.
In between, along Asia's southern tier, smaller countries are developing sea denial capabilities, though on a more limited scale. Japan has enhanced its underwater surveillance systems in response to constant intrusion by Chinese submarines into its territorial waters. More recently, it has enacted new laws to give Japan's military a wider international role.
Japan, South Korea, Singapore, Indonesia, Australia and Pakistan have all embarked on programs to upgrade, enlarge and enhance the capabilities of their submarine fleets, while Malaysia and Vietnam have begun to acquire submarine capabilities they previously did not possess.
Asia's narrow seas are becoming crowded with increasingly effective military hardware. The tangle of risks grows ever tighter as the chance of accident and confrontation rises in step with the number of submarines, ships and surveillance aircraft. In this cauldron of rivalries, suspicions and new capabilities, the era of unquestioned American sea command has come to an end.
Michael Wesley is professor of international relations and director of the Coral Bell School of Asia Pacific Affairs at The Australian National University. This article is an edited extract from his latest book, "Restless Continent," launched by Australian Foreign Minister Julie Bishop Sept. 14.