Japanese Prime Minister Shinzo Abe is now following through on actions laid out in his recent bold speech calling for Japan to defend allies who might be under attack.

But wait, you may ask, hasn’t the United States had a mutual security treaty with Japan for more than half a century?

Well, not quite. Yes, Washington has had a mutual defense-security treaty with Tokyo since 1951. But Japan is not committed to defending the United States or any of its armed forces. In fact, Japanese forces are prohibited from helping Washington in time of war — even if the war is in defense of Japan.

This goes back to the postwar U.S. Occupation of Japan and the creation of the Japanese constitution. Determined that Tokyo would never again pose a threat to its Asian neighbors or the United States, Occupation leader General Douglas MacArthur and his staff were sympathetic to Japanese pacifists’ proposal to include a no-war making article in the constitution, then being written with oversight by the Occupation authorities. This worked with the policies of then-Prime Minister Shigeru Yoshida, who wanted to focus on rebuilding the Japanese economy — without the distraction of creating a major defense force.

So Japan’s constitution prohibits engagement in war. Despite using the term “mutual” to describe the U.S.-Japan agreement, there has never been anything mutual about it. It has always been a unilateral U.S. guarantee of Japan’s defense.

This has long suited the U.S. foreign policy leadership, both Democratic and Republican. Washington has preferred to direct a forward defense against possible threats instead of relying on possibly pesky allies. It uses Japan as its most important forward base — particularly for the Seventh Fleet, which patrols Asian and South Pacific waters. The U.S. security community has therefore largely supported Japan’s pacifist policies — while quietly urging that the constitutional interpretation be broadened to allow more support for U.S. and U.N. peacekeeping efforts.

This may have been the right policy for Washington to pursue when the U.S. economy made up about 50 percent of the global gross domestic product; when U.S. military dominance in the Asia-Pacific region was absolute, and when U.S. and Japanese interests more or less coincided. But that situation no longer prevails.

The U.S. economy is now roughly 22 percent of global GDP, on the way to perhaps 15 percent. Relative military power has also shifted. The Pentagon, for example, would not today sail two aircraft carriers into the Taiwan Straits between China and Taiwan as it did in 1995, at a time of tension between Taiwan and mainland China. Nor do U.S. and Japanese interests coincide to the same extent.

Consider, the unoccupied Senkaku Islands, administered by Japan but whose Japanese ownership is disputed by China. These barren rocks are of no strategic or economic value to the United States. Yet, Washington could find itself going to war with China over them because of the peculiarities of the Japanese constitution and the U.S.-Japan security relationship.

Abe’s moves are likely to be greeted with suspicion, even violent opposition, by many in Asia. Some in the United States may also resist it. This is partly because of the still-festering wounds of World War Two and political expedience in Asia. But it is also due to U.S. concerns about Abe’s past as a right-wing, somewhat anti-American politician.

These concerns, however, should not impede U.S. support for the prime minister’s proposals. Washington does not have to agree with everything Abe says in order to support him when he says something that makes sense.

There is a growing risk that Washington may be drawn into confrontation with Beijing as a result of parochial issues between China and some U.S. allies. Japan, by taking greater responsibility for its own defense and that of its allies, would be moving to decrease this risk of having to put more Americans in harm’s way.

Washington should not only support this — it should welcome it. Despite the inevitable howls from some Asian capitals.

PHOTO (TOP): Members of Japan’s Self-Defence Forces’ airborne troops stand at attention during the annual SDF troop review ceremony at Asaka Base in Asaka, near Tokyo, October 27, 2013. REUTERS/Issei Kato

PHOTO (INSERT 1): Japanese Prime Minister Shinzo Abe speaks during a news conference at his official residence in Tokyo, May 15, 2014.REUTERS/Toru Hanai

PHOTO (INSERT 2): Members of Japan’s Self-Defence Forces’ infantry unit take part in the military’s review during the annual troop review ceremony at Asaka Base in Asaka, near Tokyo, October 27, 2013. REUTERS/Issei Kato