Japan has just christened its largest warship since World War II—a brawny helicopter carrier seemingly tailor-made for defending an archipelago nation. This follows Japan's first increase in year-to-year military spending in 11 years and first troop-strength increase in 20 years. Nearly 90 percent of Japan's lower house now supports Prime Minister Shinzo Abe's plan to lift post-World War II restrictions on military action by Japan's Self Defense Forces (JSDF). In short, Japan is reawakening to the responsibilities of regional security. This policy path is right for Japan and good for the United States.
Before getting into what the reawakening means for Japan and its allies, it's important to discuss what roused Japan from its long slumber: China, specifically, China's passive approach to North Korea and aggressive approach to the rest of the region.
On a percentage basis, the growth in military spending by China in the past decade is unparalleled: from $20 billion per year to around $180 billion per year. Fueled by that spending binge, China now deploys 79 principal surface combatants, 50 submarines, scores of ship-killing missiles and a growing armada of high-tech warplanes. Beijing is brandishing these assets to extend its reach, undermine the territorial claims of its neighbors and take control over oil-rich areas in a fait-accompli fashion.
In August, for example, four Chinese ships loitered in Japanese-administered waters for 28 hours. The New York Times notes that such incursions are taking place "almost daily."
In February, Tokyo reported that a Chinese frigate used its weapons-targeting radar to "paint" a Japanese ship in disputed waters. Plus, China is seeding waters near Japanese islands with sonar buoys, apparently to monitor Japanese submarine activity.
Chinese aircraft encroached on Japanese airspace 83 times in 2011. Japan was forced to scramble fighter-interceptors 91 times in the fourth quarter of 2012 alone, according to The Wall Street Journal. In July, Chinese planes were at it again near Okinawa , triggering a response from the JSDF—and opening the door to miscalculation and escalation. As a Japanese Defense Ministry report  warns, "China's military trend includes high-handed actions that could trigger unforeseen situations."
Worryingly, Beijing's rhetoric is as bellicose as its behavior. In 2012, Hu Jintao, then-president of China, called on the Chinese navy to "make extended preparations for military combat." His successor, Xi Jinping, declares, "We must insist on using battle-ready standards in undertaking combat preparations, constantly enhancing officers' and troops' thinking about serving in battle, and leading troops into battle and training troops for battle."
North Korea is doing more than simply talking about war. Since 2010, North Korea has shelled a South Korean island, torpedoed a South Korean warship, conducted long-range missile tests, detonated a nuke, threatened nuclear strikes against the U.S. and warned Japan  that it is "always in the crosshairs of our revolutionary army...the spark of war will touch Japan first."
In short, given that Japan's nearest neighbors are a leftover Cold War time-bomb that could explode at any moment and a rising behemoth intent on buying, blustering or bullying its way to regional primacy, no one should blame Japan for strengthening its military and redefining what its military is permitted to do.
These two very different threats—China's chess-like encroachment onto Japanese territory and North Korea's volatile unpredictability—have convinced Japan that it's time to shrug off six decades of postwar pacifism. Of course, there has been an asterisk attached to Japan's pacifism for many years. After all, Japan fields one of the most sophisticated militaries on earth: mid-air refueling aircraft, F-15 fighter-bombers, ground- and sea-based missile defenses, power-projecting warships like the new helicopter carrier, and soon next-generation warplanes like the F-35 stealth fighter-bomber. (Tokyo will take delivery of 42 F-35s in 2017.)
Put another way, although Japan had the economic means and technological muscle to play a lead role in regional security, it lacked the mindset—until now.
Abe is embracing this role with gusto. As he challenges his nation to make military, budgetary and constitutional adjustments, he has pursued deeper partnerships with other democracies in the region. Abe envisions "a strategy whereby Australia, India, Japan and the U.S. state of Hawaii form a diamond to safeguard the maritime commons," and he is eager "to invest, to the greatest possible extent, Japan's capabilities in this security diamond."
Japan and India have agreed to joint naval exercises and resource-development projects . Japan and Australia signed a bilateral declaration on security cooperation in 2007 and a defense-acquisition agreement in 2010. Japan and South Korea conducted unprecedented joint air maneuvers  in August under the auspices of the U.S.-led Red Flag Alaska. And Japan is helping rebuild the Philippine military. Tokyo has pledged Manila 12 new cutters, and the former foes recently signed a long-term military-cooperation agreement enfolding exchanges of personnel and technology. Most remarkably, Manila is open to Japanese troops deploying to the Philippines .
But no partnership is more important to Japan than its enduring partnership with America. Tokyo calls the U.S.-Japan alliance one of the "pillars of Japan's national defense." Similarly, President Obama describes the alliance with Japan as a "cornerstone" of America's security.
To extend the architecture metaphors, the U.S.-Japan security scaffolding is bearing an increasingly heavy load, as the U.S. military shifts its focus to the Asia-Pacific region and Japan faces up to a range of new threats.
With China's military power increasing and with sequestration diminishing  America's military power, Washington needs Japan to do more in the security arena. And with Japan shouldering a larger security burden, Tokyo needs American cover (to reassure Japan's neighbors) and American guidance (to steer the JSDF into the new terrain of overseas engagement).
That explains this month's updates  to the U.S.-Japan military alliance—updates that allow for the basing of U.S. drones and maritime reconnaissance planes in Japan, outline the creation of a U.S.-style National Security Council for Japan, and warn that the allies will respond to "coercive and destabilizing behaviors" by regional bullies.
It also explains training operations like Dawn Blitz in July, which brought a thousand Japanese troops to California to learn the finer points of amphibious warfare. The Wall Street Journal reports that maritime threats and the 2011 tsunami have convinced Tokyo that it may be time to stand up a special division within the JSDF modeled after the U.S. Marine Corps. If the lessons of the Cold War are any guide, such a force would help deter—not trigger—war.
Speaking of deterrence, Adm. Robert Willard points to a trio  of "burgeoning trilateral relationships" as essential to keeping the Pacific, well, pacific: the U.S.-Japan-ROK partnership, U.S.-Japan-Australia partnership and U.S.-Japan-India partnership. It's no coincidence that the common ingredient to each—and to a peaceful Pacific—is the bond between the United States and Japan.