It took Ronald Reagan and Mikhail Gorbachev years to negotiate it, but only a day for the Trump administration to leave behind the hard-fought nuclear arms reduction treaty the U.S. and Russian leaders signed more than 30 years ago.

Twenty-four hours after the U.S. withdrew from the Intermediate-Range Nuclear Forces Treaty, the first to eliminate an entire class of weapons, U.S. Secretary of Defence Mark Esper said he'd like to put ground-based, intermediate-range conventional missiles in the Asia-Pacific region within months.

It confirmed what many had suspected was the motivation for exiting the treaty, which was signed in 1987 and banned all land-based ballistic missiles, cruise missiles and missile launchers with ranges of 500 to 5,500 kilometres.

While ostensibly a reaction to Russia's flagrant violation of the treaty as far back as 2011 , when the U.S. first got wind it was developing an intermediate-range cruise missile known as 9M729, or SSC-8, it was also an opportunity for the Trump administration to exit an agreement it saw as an artefact of the Cold War that no longer met its defence needs.

Old ways weren't working

In the administration's view, a treaty drafted more than 30 years ago with the protection of Europe in mind was now hampering its ability to counter China's expanding military power, specifically, its acquisition of the intermediate-range missiles the treaty barred the U.S. and Russia from owning.

"So, the United States is looking at this overall situation and saying, 'Why are we continuing to be self-limited by adhering to a treaty that was put together for a different era and a different set of challenges?'" said Dakota Wood, senior research fellow for defence programs at the D.C.-based think-tank the Heritage Foundation and a retired lieutenant-colonel in the U.S. Marine Corps.

U.S. Secretary of Defence Mark Esper, pictured on the parade grounds at the Pentagon last week, said Saturday that he'd like to put ground-based intermediate-range missiles in the Asia-Pacific region. (Mark Wilson/Getty Images)

Russia's recent brash interventions in Europe — incursions into parts of Georgia and Easten Ukraine, annexation of Crimea and increased military presence on the border with the Baltic States — didn't bolster the case that the treaty was an effective deterrent either, Wood said.

"From the current administration's perspective, how did the old ways of doing things work out? And their conclusion is it didn't work out too well.

"Diplomacy not backed by credible military power and the threat of its use really gave free rein to an actor like Vladimir Putin."

A 9M729 land-based cruise missile in Kubinka, outside Moscow, is shown on Jan. 23. The U.S. says Russia continued to develop such intermediate-range missiles in contravention of the INF treaty despite repeated warnings. (Pavel Golovkin/The Associated Press)

Defence experts disagree on whether the U.S. needs land-based intermediate-range missiles to counterbalance China's growing arsenal or could continue to rely on existing short- and long-range missiles deployed from ships and planes. There is also the question of how eager its allies in the region will be to host the missiles.

In terms of nuclear capacity, China, with its less than 300 warheads, lags far behind the U.S. and Russia, which each have more than 6,000, but it has been increasing its stockpile of conventional intermediate-range missiles that are mobile and can be launched quickly from the ground.

The U.S. already signalled earlier this year, after it announced in February it would withdraw from the INF treaty if Russia didn't return to compliance within six months, that it would begin testing new missiles this summer if the agreement did collapse.

Now, some worry the termination of the treaty may signal the start of a new arms race.

When U.S. President Ronald Reagan, right, and Soviet President Mikhail Gorbachev signed the Intermediate-Range Nuclear Forces treaty at the White House on Dec. 8, 1987, it broke the impasse in nuclear disarmament negotiations, which had been hindered by Reagan's pursuit of the Strategic Defensive Initiative, a ballistic missile defence system. (Dennis Paquin/Reuters)

U.S. had other options, say critics

Not everybody thinks it was necessary to scrap a treaty that had successfully taken more than 2,600 nuclear weapons out of commission to send a signal to Russia and make the geopolitical pivot to the Asia-Pacific region.

"There were plenty of other options available to the United States while remaining a party to the treaty: Diplomatic, economic and military options that could have been pursued to continue to put pressure on Russia to return to compliance and ensure that Russia didn't gain a military advantage by virtue of its violation," said Kingston Reif, director for disarmament and threat reduction policy at the Arms Control Association in Washington, D.C.

The INF treaty doesn't limit cruise missiles launched from the air or sea, so the U.S. could have deployed some of those to the European theatre as a show of strength or beefed up its missile defence systems and deployed land-based missiles with a range of up to 500 kilometres, he said.

"Now, we're in a situation where the bilateral U.S.-Russian arms control architecture, which has long been a linchpin of international peace and security and has helped to reduce the risk of nuclear conflict, is on the verge of collapse."

The U.S. Navy Arleigh-Burke-class guided missile destroyer USS Curtis Wilbur launches a harpoon surface-to-surface missile during Pacific Vanguard quadrilateral exercises between Australia, Japan, South Korea and U.S. Naval forces in the Philippine Sea on May 26. Some argue sea- and air-based missiles are enough to handle the military threat of China. (Toni Burton/U.S. Navy/Reuters)

Europe anxious about what future holds

Russia has for years argued that the ballistic missile defence system the U.S. installed in Europe undermines its nuclear deterrence capabilities, despite assurances that it's intended to ward off missile threats from Iran.

But there are any number of reasons why Russia may have violated the treaty, Reif said. It may have wanted to enhance its regional strike capabilities within Europe in the face of NATO's eastward expansion or to have a land-based mobile missile system that would be more difficult to destroy in a larger conflict with NATO. Or it might have been simply a case of missile envy among the army, air force and navy factions within its military.

"None of those reasons justified, in my view, walking away from the treaty on Russia's part," Reif said.

The US and NATO agree: Russia violated the INF, and leaving the agreement is in the best interests of our collective security. Treaties are worthless unless respected by all signatories. <a href="https://t.co/tqh1zGz9Sl">https://t.co/tqh1zGz9Sl</a> —@SecPompeo

The treaty was designed to protect NATO allies in Europe and, although the official statement from NATO's secretary-general backed the U.S. decision and said "Russia bears sole responsibility for the treaty's demise," individual nations are justifiably nervous.

"With the end of the INF treaty, Europe is losing part of its security," German Foreign Minister Heiko Mass said Friday.

In February, at the first signs of a U.S. exit, EU foreign policy chief Federica Mogherini said, "What we definitely don't want to see is our continent going back to being a battlefield or a place where other superpowers confront each other."

One more treaty on the chopping block

Domestically, the treaty withdrawal comes at a time of intense scrutiny of U.S.-Russia relations.

While on the one hand, Trump has fostered a relationship with Russian President Vladimir Putin and is accused of welcoming the country's interference in the 2016 election and safeguarding of his business interests there, the U.S. has also pursued punishing sanctions — as recently as this week — and other hostile measures against Russia.

"You have, on the one hand, whatever Trump himself wants, but then you have a Congress that's passed very tough legislation on Russia and an executive branch ... that's also put through much tougher policy," said Angela Stent, author of Putin's World: Russia Against the West and With the Rest and director of the Center for Eurasian, Russian and East European Studies at Georgetown University in Washington, D.C.

Russian President Vladimir Putin hasn't shown much interest in preserving the New START treaty limiting long-range missiles, which is set to expire in 2021 unless U.S. and Russia extend it. (Aleksey Nikolskyi/Sputnik/Kremlin/Reuters)

"There are a lot of contradictions. The Trump administration doesn't have a coherent policy toward Russia."

On a global scale, it's another in the series of international agreements the U.S. has walked away from in the last three years and will join NAFTA, the Trans-Pacific Partnership, the Paris climate agreement and the Iran nuclear deal on the scrap heap.

"It fits into this pattern that the Trump administration isn't interested in treaties that could be seen as constraining American power," said Matt Korda, a research associate at the Federation of American Scientists, which tracks countries' nuclear arsenals and advocates non-proliferation.

What about the New START treaty?

The most immediate concern in the wake of the collapse of the INF is what it might mean for the New Strategic Arms Reduction Treaty (START), the sole remaining arms control agreement limiting U.S. and Russian nuclear forces.

New START was signed by former U.S. president Barack Obama and his Russian counterpart, Dmitry Medvedev, in 2010 and caps the number of long-range nuclear weapons Russia and U.S. can have.

It's set to expire in 2021 and can be extended by five years, although National Security Adviser John Bolton said in June that is "unlikely" to happen.

Bolton has complained New START doesn't include short-range and tactical weapons, which Russia has more of than the U.S., and told the National Conservative Student Conference this week, "Why extend a flawed system just to say you have a treaty?"

"I think that's a pretty strong signal that this treaty is in serious trouble," said Stent.

U.S. President Barack Obama and Russian President Dmitry Medvedev sign the new Strategic Arms Reduction Treaty at Prague Castle on April 8, 2010. The treaty is now the sole remaining nuclear arms control agreement regulating the two powers that control 90 per cent of the world's nuclear arsenal. It's set to expire in 2021 unless the two countries extend it by five years (Jason Reed/Reuters)

Bolton and Trump have both said they want a nuclear pact that includes China and other nuclear powers, but some question how serious they are about pursuing it.

"Is that a worthwhile objective? Yes. Does the administration have the plan or the capacity to negotiate such a comprehensive and quite frankly unprecedented agreement? No," Reif said.

Even if it did, it certainly wouldn't happen before 2021.

"[Extending] New START would buy five additional years of stability, predictability and transparency in the U.S.-Russia nuclear relationship, which is much needed right now, given where we are, and also lay a foundation to pursue a more comprehensive approach," Reif said.

Russia itself has shown little interest in extending the treaty or encouraging the U.S. to do so.

"The Russians have already said that they understand that this might happen, and if that happens, so be it," Stent said. "The really dangerous thing then is, you lose any ability of either side to verify and monitor what the other side is doing."

New class of weapons

While Russia and the U.S. still have about 90 per cent of the world's nuclear weapons stockpile, the threat today is multipolar, with different nuclear-armed countries embroiled in their own regional tensions, said Korda.

"It's really easy to see a situation in which a conflict between India and Pakistan, for example, can spiral out of control. It's really easy to see how China could get looped into that and then how the United States could get looped in and then Russia."

The Agni II, an intermediate-range ballistic missile, is rolled out during the Republic Day parade in New Delhi on Jan. 26, 2002. Any attempt to extend a nuclear treaty to other countries, such as India, Pakistan and China, would be a tall order. (Pawel Kopczynski/Reuters)

The type of nuclear weapons countries have is also expanding. Russia recently showed off the Poseidon, a 24-metre nuclear-enabled torpedo that would, Russia claims, create a radioactive tsunami.

The threat, Reif says, has expanded to include hypersonic conventional missiles that travel at five times the speed of sound and can potentially target nuclear arsenals and cyberweapons that can sabotage nuclear command and control systems.

Russia and U.S. were already in the process of modernizing their nuclear arsenals before the treaty collapsed.

"I do think that what you're going to see now with the U.S. out of the INF treaty is, you know, a new class of weapons or an upgrading of some older weapons like the Tomahawk, which could be then directed against China," Stent said.

The massive destructive potential of nuclear weapons and the speed with which they can be deployed have long served as a deterrent, but as Russia, the U.S. and China pursue so-called lower-yield nuclear weapons, which still have the capacity to kill tens of thousands of people, some fear the threshold for using them is getting lower.

"The threshold still remains very high, but even a small diminution of that threshold given the destructive power of nuclear weapons is significant," Reif said.