Ever since the US entered World War II, one of the mainstays of its power and influence in the world – at least in the security realm – has been its willingness to provide military support to those governments seeking it in the face of common adversaries.
The US has done this successfully in several instances, such as in World War II against the Axis powers, during the Korean War against North Korea and its communist allies, through the Cold War generally against the Soviet Union and its many allies, in the 1991 Persian Gulf War against Saddam Hussein, and up to now in the war in Ukraine against Russia. In these instances, demand for US military support was met with supply, though in the case of Ukraine this has been limited to a US arms supply and not military intervention.
There have also been, as is well known, instances in which the US intervened militarily to defend weak allies, but then withdrew its forces and those allies fell. These include Indochina in the early 1970s and Afghanistan in 2021. In these cases, the US reduced or even ended its supply of military support despite continued demand from governments (if not their citizens) previously receiving it. These experiences led to grave doubts on the part of other US allies whether Washington would sufficiently supply their demands for military support.
During his first term as president (2017-21), Donald Trump raised doubts about whether the US would defend NATO and other US allies that were not spending as much as he thought they should on defense. By saying this, some believe, Trump was making a ploy to get NATO allies (among others) to spend more on defense – something which every previous president since Eisenhower had also sought. During his 2024 campaign, Trump has again raised the prospect that the US won’t defend allies not spending what he considers enough on defense, and that he might even seek to withdraw the US from NATO.
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Many Republicans in Congress have joined with Democrats to ensure that Trump cannot do this on his own. But following the initial wave of bipartisan support for Ukraine after it was attacked by Russia, more and more Republicans – especially in the House – have expressed opposition to continued US support for Ukraine. It is currently unclear whether Trump, if re-elected, will continue supporting Ukraine to the same level of the Biden Administration, if at all. Kamala Harris shares Biden’s desire to continue backing Ukraine, but her ability to do so as president could be limited in the event of a Republican-controlled House.
Should the US presidential and congressional elections result in diminished US supply of military support to Ukraine and Russia then prevails against it, there are several possible consequences, as follows:
- Dictatorships are emboldened to launch attacks elsewhere
If the US does not continue supplying arms to Ukraine so it can defend itself, dictators might conclude that the US would not do so elsewhere, let alone intervene militarily. A defeat for Ukraine could raise the prospect of China invading Taiwan, Iran and its allies increasing their attacks on Israel and the Arab Gulf states, and Russia itself invading other countries.
- US allies (among others) acquire nuclear weapons
One important reason why most US allies have not acquired their own nuclear arsenal is that the US “nuclear umbrella” they have sheltered under has meant they have not had to do so. Although never sure that the US would use nuclear weapons to defend them, the fact that their adversaries have not invaded them suggests that US nuclear weapons – along with conventional ones – have had deterrent effects.
But the more US allies doubt that America will defend them either with its nuclear or conventional forces, the more likely it is that some US allies will see acquiring their own nuclear arsenal as an increasingly necessary means of deterring invasion. And more countries acquiring nuclear weapons increases the likelihood that others will follow.
- US allies make “other arrangements” such as alliances among themselves
Such alliances would likely be comparatively weak without US participation. They may well be more regionally based and focused on a specific adversary, such as the EU developing a defense capacity against Russia; Asia-Pacific nations (Japan, South Korea, Australia, New Zealand, the Philippines, and perhaps Taiwan) cooperating against China; and Gulf Arab states and Israel (even if not in a formal alliance) against Iran.
These alliances, though, may not cooperate much with one another, and may even compete for what limited attention a US in retreat is willing to devote to international security. To this end, some NATO members are likely to seek bilateral security agreements similar to those in place for non-NATO countries such as Japan and the Philippines.
- Some US allies might cozy up to US adversaries such as Russia and China
As we have already seen with Viktor Orban in Hungary vis-a-vis Russia, some allies may decide that they are better off band-wagoning with US adversaries they think have a greater chance of prevailing. Some in Europe may calculate that if they cannot depend on the US to protect them from Russia, then perhaps they should cozy up to China in the hope that Beijing can restrain Moscow. Needless to say, such hopes may prove unrealistic.
- Conflict spreads
A curtailment of US security assistance may not just embolden America’s adversaries but may also embolden less democratic allies to undertake military adventures that they might not otherwise have launched. In fact, some US allies might decide that, for defensive reasons, they need to strike first before emboldened adversaries or erstwhile allies inevitably (they may believe) attack them.
- Shifting dynamics of power and influence
US domestic politics could increasingly become an arena for foreign powers who see their competitions with one another as being significantly affected by either getting the US to resume its supply of security assistance or preventing it from doing so.
Still, some might argue that the reduction of US security assistance to its allies does not necessarily mean that US influence would not persist economically. The EU, Japan, ASEAN, OPEC, and others have shown that economic influence can be great even when military power is limited or not exercised. Still, these others have exercised their economic influence – sometimes even in competition with the US – while receiving American military support and protection in some form.
In the absence of any other benevolent great power emerging that can take up the burden of supplying security support if the US is unwilling to continue doing so, America and its allies may find that rising adversarial powers will be in a better position to further their own economic interests at the expense of the US and its allies.
There is always the possibility, of course, that even after stepping back from providing its allies with security assistance, the US could later resume this role, just like how the American retreat into isolationism after defending its European allies in World War I was followed by America intervening to defend them – as well as others – in World War II.
But just like it was then, it may be very costly to do so, and America may not be as successful at this as it was in World War II.
America and its allies, then, would be a lot better off if the US didn’t retreat into isolationism again now and be faced with the possibility of having to enter a very costly war to prevent the world from becoming dominated by hostile dictatorships. Such a war would be no guarantee of Western success. It would be far better not just for America’s allies, but for America itself, if the US continued to supply the security assistance that its allies continue to demand.
Mark N. Katz is a professor emeritus of government and politics at the George Mason University Schar School of Policy and Government, a global fellow at the Wilson Center, and a nonresident senior fellow at the Atlantic Council.
The views expressed are the author’s and not necessarily of Kyiv Post.
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