When armed forces "pivot," it can mean a lot.

"General Douglas MacArthur, the 'The Hero of Bataan,' has arrived in Australia. ... This is mighty interesting news to all of us," wrote war correspondent George H. Johnston in 1942. "It shows at least that this zone of defense is to be given its proper importance."

The Australians got more than MacArthur. In the months ahead, the U.S. reinforced the island continent with planes, troops and supplies that turned the course of World War II in the Southwest Pacific.

At the start of the war, Washington had publicly marked Hitler's Germany as the focus of our "main effort." Yet during the first two years of the conflict, we actually sent more men and material to the Pacific theater. It was necessary to keep America from being pushed out of the region permanently.

Strategy is about making tough choices. And tough choices always involve putting money -- and muscle -- where it is most needed. And there's the challenge.

In World War II, America had to figure out how to fight a two-front war. Today, the U.S. is a global power. To protect its global interests, Washington must figure out how to deal with security threats on virtually every continent.

Yet President Obama would have us believe we can assure global stability by dealing with threats sequentially. Proclaiming the war on terrorism pretty much "won" in the Middle East, in the fall of 2011, he announced a "pivot to Asia."

It was intended to sound smart. But reality has yet to match the rhetoric.

For example, Obama trumpeted the planned build-up of a Marine base in Australia. Yet the anticipated size of the build-up is quite modest. And often these Marines would simply rotate in from other Pacific locations. The "commitment" resembles a "shell game" more than a real increase in capability.

Now, there is even doubt that the Australian "build-up" will ever materialize. Negotiations between the Yanks and the Aussies are not going smoothly. A cynic might suggest that we've seen this before.

The White House found Iraqi leaders conveniently unwilling to cut a deal that would keep American troops in-country, and--voila--Obama got what he really wanted: zero troops in Iraq.

Negotiations with Afghanistan aren't going well, either, so Obama may get his zero option there, too. If Canberra doesn't come around ... well, maybe it's the zero option for Australia.

All these "failures to cooperate" have one thing in common: They are convenient for the president. They allow him to withdraw America from the world, and no one can say it's his fault. Heck, he tried to stay engaged, but "they" wouldn't let him.

And continuing disengagement makes deeper cuts in defense seem more defensible. So what if we lose 30 Navy ships? We don't need to be in the Strait of Hormuz. Why build more F-35s? No need to defend airspace over Afghanistan anymore.

Zero options make it easier for Obama to do less in the defense of the nation and its interests.

Granted, the U.S. doesn't need bases and troops everywhere in the world. But we need them in every region where our military may be expected to operate. The southwest Pacific is one of those regions.

In time, U.S. and Australian negotiators may well work out their differences. Ultimately, as many as 2,500 Marines may deploy to Darwin. That's a modest commitment, at best, but it's emblematic of Obama's attempt to protect America with a force too small for the big world it has to cover.

JAMES JAY CARAFANO, a Washington Examiner columnist, is Vice President for Defense and Foreign Policy Studies at the Heritage Foundation.