Besides the North Atlantic Treaty, the US is a party to the Australia-New Zealand (ANZUS) defense treaty, the Philippine treaty, the Japanese treaty, the Republic of Korea treaty, and the Southeast Asia treaty, singed back in 1954 by United States, Australia, France, New Zealand, Philippines, Thailand, and the United Kingdom.
In addition, Washington has less formal longstanding relationships with Israel and the Gulf nations.
"The value of US alliances should be judged on their contribution to US security — the ability to defend the safety, sovereignty, and territorial integrity of the United States… [However] in no case do current allies directly 'defend' the United States, though some do occupy important strategic geography, which contributes to our military power. At best, our allies defend themselves with vast assistance from the United States," Barry R. Posen, Ford International Professor of Political Science of the Massachusetts Institute of Technology, writes in his article for the National Interest.
Interestingly, the US military costs are usually minimized by Washington's security architecture proponents, the scholar notes, arguing that the US could have cut a fifth of its defense budget — about one hundred billion dollars — if Washington was "more judicious in its promises abroad."
However, the US foreign policy establishment is calling for a more muscular and tough policy toward the Middle East and Russia that actually means that Washington should spend even more money on wars for the sake of its foreign partners.
When it comes to the US' nuclear commitments to its allies, Washington may eventually find itself on thin ice.
To defend its partners in Europe and Asia from their potential adversaries, the US must signal to those potential challengers that "it would, if pressed, wage nuclear war" on behalf of its allies, the scholar explains.
"Are these nuclear commitments strategically necessary?" Posen asks.
Is the US really ready to wage an all-out nuclear war to defend its allies in Europe or in Asia?
To make matters even worse, the US' "extravagant insurance" that Washington offers its partners "encourages them to engage in risky behavior," he emphasizes.
"The strategic benefits to the United States of its NATO commitments are thus slim," the US academic believes.
He recalls that NATO was founded as a defense alliance aimed against the USSR in the first place. However, Russia does not pose a similar "threat" to Europe today, he underscores.
"We are treated to tales of Russian and Chinese threats to the 'rule based international order.' This 'order' is simply the military alliance and trading system that the United States built to wage the Cold War, and which the foreign-policy establishment assumed upon the end of that great struggle would naturally grow to encompass all the other countries of the world," Posen elaborates.
It is also unsurprising that Trump immediately came under fierce criticism from the US foreign policy establishment for his remark.
"Donald Trump shocked foreign-policy professionals and observers when he remarked to The New York Times that if he were president, the United States might not come to the defense of an attacked NATO ally that hadn't fulfilled its 'obligation to make payments.' The remark broke with decades of bipartisan commitment to the alliance," Nicholas Clairmont of the Atlantic underscored.
Meanwhile, 50 Republican national security experts have recently signed an open letter that lambasts the Republican nominee.
"Mr. Trump has demonstrated repeatedly that he has little understanding of America's vital national interests, its complex diplomatic challenges, its indispensable alliances, and the democratic values on which US foreign policy must be based," the letter reads as quoted by Reuters.
Although Trump has obviously hit the US establishment's raw nerve by his remark, it is most likely that both the Democratic and the Republican nominees will remain committed to the US alliance system, Posen predicts, adding that in any event Obama's successor "will be forced to revisit real defense burden sharing."