Is it time to junk the security architecture of Northeast Asia, which has been in place for nearly 60 years, with a new and genuinely mutual "triple alliance" between Japan, South Korea and the United States? The three nations have been making tentative but unmistakable steps in that direction.

Last month, for the first time, South Korea sent military observers to take part in joint US-Japan military exercises held at several places off Japan's coast. Earlier, members of Japan's Self Defense Forces observed similar exercises between the South Korean and US navies held in response to the sinking of a Korean naval corvette.

Adm. Mike Mullen, Chairman of the U.S. Joint Chiefs, has called on the two Asian nations to take things farther by hosting three-nation exercises in the future with the US. Japan's hawkish foreign minister Seiji Maehara has said that his nation's military ties with South Korea will slowly increase in response to provocations from North Korea.

The first concrete steps were taken in early July when Tokyo and Seoul negotiated their first military agreement following talks between the two nation's defense ministers. The accords covered mutual cooperation and assistance in gathering intelligence, especially on North Korea, and sharing supplies on peacekeeping missions abroad.

These steps are far, far from being a mutual defense alliance, but they show the direction things are moving and how concerned the three potential "allies" are about the provocations by North Korea last year, including November's murderous shelling of an offshore island, not to mention North's growing nuclear arsenal. Add to that, growing concerns about the expanding and modernizing Chinese navy.

But one might ask: are not South Korea and Japan already allies of the US? The answer would be yes and no. Washington has formal security arrangements with both countries on a bilateral basis, but a closer look shows that the two arrangements are very different, reflecting the security situations as they have developed since the end of World War II.

The Treaty of Mutual Defense between South Korea and the US was signed in 1953 only a few months after the end of the Korean War when the northern invasion was fresh in everybody's minds. It is a true alliance in that both sides promise to come to the aid of the other in the event of an attack.

The US still bases approximately 28,000 troops and other military assets in Korea. An American four-star general heads the Combined Forces Command and would, in an attack, assume direct command of both the American and Korean forces (this is set to change in 2012 after which a Korean general would be placed in charge.)

Since 2005 the official mission of American forces based in Korea has changed. The forces are no longer there just to serve as a "trip-wire" in the event of a North Korean invasion (in other words, ensuring American help as they would be in the thick of fighting from the beginning). Under a policy known as "strategic flexibility," they could be deployed outside of Korea to meet other contingencies – such as a Chinese invasion of Taiwan.

The so-called alliance with Japan is not really an alliance at all. It is basically a deal: the U.S promises to defend Japan if attacked, with nuclear weapons if necessary (the so-called nuclear umbrella). In return Japan grants American forces bases on its territory to use pretty much as Washington sees fit in advancing US national interests.

One could see how this works this last fall when the aircraft carrier George Washington and its escorts, based at Yokosuka near Tokyo, deployed in the Yellow Sea for joint exercises with South Korea, showing that, unlike Japan's indigenous "Self-Defense" forces, the American forces are not deployed strictly to defend Japan.

On the other hand, Japan has no treaty obligation to help the US defend itself. Thus should North Korea launch a ballistic missile over Japan toward the US, as it has done twice in the recent past, the Japanese would not be obliged to try to shoot it down. Indeed, it would be technically illegal under its constitution.

This scenario is not just a theory. Secretary of Defense Robert Gates himself has warned that North Korea could possess a ballistic missile capable of reaching Alaska in the next five years. It is not clear whether the North has the technical ability to fashion nuclear warheads on them as opposed to exploding bombs in simple underground tests.

Japan's pacifistic constitution (written by post-WWII American occupiers) has been interpreted to preclude "collective defense." That means the document would have to be amended or reinterpreted in for Japan to enter into a full-fledged alliance with either South Korea, the US or both.

Far from being integrated into a single command as in Korea (or Europe under NATO), the Americans in Japan and the Japanese armed forces might as well have inhabited different planets for most of the past 50 years. It is only recently that the two countries have gradually moved to integrate their forces and hold exercises together.

There are obvious barriers in Japan allying itself with South Korea, not the least being lingering memories Koreans have of Japan's long occupation of the Korean peninsula. The two countries also dispute ownership of a small group of rocky islets in the Sea of Japan (East Sea to Koreans) called the Dokdo by Koreas and Takeshima by the Japanese.

The Japanese too are puzzled and vaguely threatened by South Korea's apparent desire to build a "blue-water" navy. In 2007 South Korea commissioned its largest warship, a helicopter amphibious assault ship with the pregnant name of Dokdo. What use are these amphibious ships in defending against a northern invasion, they wonder? (The Koreans say they are useful in peace-keeping and disaster relief).

Shortly after assuming office last June Japan's Prime Minister, Naoto Kan, issued a formal Japanese apology on the 100th anniversary of Japan's annexation of Korea in 1910, which may help ease Korean suspicions. It may be his most useful foreign policy initiative since taking office to date.

The American-backed defense and security architecture of Northeast Asia is now more than 50 years old and was conceived in a different time for different contingencies. Then the main threat, obviously, was the Soviet Union and a fear of a conventional invasion by North Korea.

The threat from Russia has receded while worries over China's rapidly modernizing military have accelerated, especially in the past year. Meanwhile, North Korea has acquired the ability to build atomic bombs and is working on the means to deliver them.