How the US military’s overseas troop deployments affect global defense spending

This post is based on the article “Regions of Hierarchy and Security: US Troop Deployments, Spatial Relations, and Defense Burdens”, by Michael Allen (Boise State University), Michael Flynn (Kansas State University), and Julie VanDusky–Allen (Boise State University), which is forthcoming in International Interactions.

Since the end of World War II, the United States has deployed tens-of-thousands of military personnel overseas. In spite of their importance to foreign policy, relatively little research has focused on understanding the effects of these deployments. However, recent years have seen an increase in research on the effects of such deployments on a wide range of outcomes, including host-state military spending (Allen, Flynn, and VanDusky–Allen 2014), the use of military force and the size of the host-state’s military (Martinez Machain and Morgan 2013), human rights (Bell, Clay, and Martinez Machain 2016), economic/human development (Jones 2012; Jones and Kane 2012), trade (Biglaiser and DeRouen 2007), and crime (Allen and Flynn 2013).[1]

While research on this subject has come a long way, these studies all typically focus strictly on the host-state itself, or on the relationship between the host-state and the United States. Our study builds on these previous works by exploring how the deployment of US military forces within the host-state (or potential host-state) interacts with deployments in the neighboring region to affect host-state foreign policy. Specifically, we focus on how troop deployments affect host-state military spending.

We argue that this represents an important step—both theoretical and empirical—in understanding how military deployments affect the states around them. Though military deployments obviously affect the host-state itself due to their presence, deployments are often made with an eye towards establishing broader regional stability and security through their deterrent effect. By establishing a large military presence in country A, the US might hope to dissuade country B from acting more aggressively. This was the basic logic underpinning US military deployments to West Germany, Japan, South Korea, and other Western European countries throughout the Cold War. So, for states like the Soviet Union, what mattered was not just the presence/absence of US military personnel within their own borders, but the presence of US military personnel in their near abroad. It is also worth noting that the projection of military power has long been central to international relations theory, but we still know relatively little about how the methods that states use beyond the use of military force. Though important, the use of military force is rare compared with the omni-present nature of US military deployments in the post-war era.

Our findings also have some timely policy implications. Recent remarks made by Republican presidential nominee, Donald Trump, suggest that his willingness to defend NATO allies would be contingent upon allied states’ contributions (presumably) to the collective defense, or perhaps more narrowly to the US. Trump has explicitly threatened to cut back on the US’ military’s overseas presence. Our results indicate that rather than free-riding on US security provisions, NATO member states have actually tended to follow the United States’ lead, increasing or decreasing defense burdens in response to increases or decreases in US military deployments to their territories and the surrounding region.

Understanding US military deployments and their effects in a spatial context

We adopt a theoretical framework based on Lake’s (1999, 2009) work on international hierarchies, and on Morrow’s (1991) work on asymmetric alliances, to help us make sense of how states respond to US military deployments in, and around, their territories. In essence, states can trade freedom of action over specific policy areas in exchange for security provided by the US. The deployment of US military forces to another country can help to ensure the security of the host-state by supplementing the host-state’s military forces, or be serving as a deterrent to would-be aggressors. This is essentially the case with West Germany and South Korea in the Cold War. Similarly, US military forces deployed abroad can help to educate and train the host-state military, thereby improving their skill and efficiency. For providing security to the host-state, the US gets increased influence over the host-state’s foreign policy, and itself gains flexibility through the use of overseas bases, airspace, ports, etc.

One method that scholars have adopted to capture this dynamic is to look at the host-state’s military spending, since higher levels of military spending should allow the host-state to assert itself and its preferences more forcefully in many areas of international affairs. The basic logic of this tradeoff suggests, then, that when the US provides greater security to a state through the deployment of US military forces, we should expect to see the host-state’s military spending go down.

Previous studies have repeatedly confirmed this dynamic. Lake (2009) finds that the host-state lowers its defense burden (i.e. defense spending as a percentage of GDP) as the size of US military deployments relative to the host-state population increases. Martinez Machain and Morgan (2013) similarly find that the size of the host-state military in terms of military personnel also decreases as the US troop presence increases. In a previous study we find that larger US military deployments correlate with a smaller host-state defense burden, but also find some evidence that these reductions in military spending go along with increases in spending on domestic programs, like education (Allen, Flynn, and VanDusky-Allen 2014).

But what about third-party states? That is, what about the states near and around the host/referent state? Essentially, the basic logic is the same. As the size of US military forces in a state increase, and the security provided by the US, we should expect that the host-state’s foreign policy to be increasingly influenced/controlled by the US. Basically, we are moving from considering a single state to a group of states, and how the status of their with the US affects each state’s foreign policy decision-making. Government leaders never make foreign policy decisions in a vacuum, and so their interactions with the US are necessarily going to be weighted by considering how their decisions will affect relations with their neighbors.

Consider two states: State A and State B. Our argument is simply that the effects of US military deployments are reinforcing. Evidence indicates that State A will lower its defense burden in response to increasing the size of the US military deployment within State A’s territory, but we argue that how much State A reduces its defense burden will depend on the troops hosted by State B. If State B hosts no US military personnel, then it may be that State A’s positive relationship with the US is not shared by State B. Though State A may reduce its defense spending, it should limit how much it cuts because State B is not similarly constrained by the US.

Alternatively, if State B also hosts a large US deployment, then its foreign policy should be constrained by the US, as is State A’s. This fact should lead State A to lower its defense burden even more than it would have were State B not hosting US military personnel. When State A’s neighbors are hosting US military deployments, and therefore their foreign policies are all more heavily influenced by the US, the need for spending more on defense is alleviated. In this case, State is in a neighborhood in which all of the residents are more closely aligned with the US.

Ultimately we expect states to reduce their defense spending when they host larger US military deployments. Further, we expect those reductions in defense spending to be larger when the host-state is surrounded by other states that host US military forces.

Evaluating the conditional effects of direct and regional deployments

We evaluate these expectations using data on US overseas troop deployments from 1950–2003. Our results generally indicate that regional deployments do indeed condition how states respond to deployments within their own territory.

Predicted defense burden as a function of direct and regional US military deployments.
Figure 1: Predicted defense burden as a function of direct and regional US military deployments.

Figure 1 succinctly shows the predicted defense burdens as a function of 1) direct deployments to the referent state (the X axis), and 2) deployments to states neighboring the referent state (the Y axis). The darker colors indicate the predicted level of the referent state’s defense burden. Focusing on states with small direct deployments (e.g. values less than 3 on the X axis) we can see that increases in the size of regional deployments increases the referent state’s defense burden. Similarly, we can see that for regional deployments of any given size, increases in the size of direct deployments to the referent state generally produce lower defense burdens. Accordingly, we find that states tend to reduce their defense burdens as the US military presence in their neighborhood increases, but do so more dramatically when they are surrounded by states that are also hosting larger US military deployments.

NATO’s Exceptionalism

The results discussed above apply to most states, but it is worth noting that our results indicate that NATO member states respond in the exact opposite way. In an earlier study (Allen, Flynn, and VanDusky–Allen 2014) we have found that NATO allies respond to increases in US military deployments to their borders by increasing their own defense burdens. In our more recent analysis, we find a similar result, but show that this response is conditional upon the broader regional distribution of US military deployments. As the US military deployment to a NATO member state increases, that member state will increase its defense burden, but this change is larger when the NATO member is surrounded by states also hosting large US military deployments.

Generally speaking, NATO member states are actually inclined to follow the United States’ lead, increasing defense spending when the US increases its own military footprint in Western Europe, and decreasing military spending as the US downsizes its European military presence. This, combined with the fact that US allies have routinely subsidized the US military presence overseas through a combination of tax cuts and direct payments, and that the presence of such overseas deployments substantially reduce the transaction costs of maintaining a global military presence and of launching overseas military operations, suggests the concerns over the exploitation of the United States by its NATO allies in particular, are overblown. Incirlik Air Force Base in Turkey, for example, both houses US nuclear weapons, and also serves as a staging area for US attacks against the Islamic State. It also suggests that US efforts to deter adversaries, like Russia, by bolstering the US’ military presence in the region, are directly supplemented by the defense efforts of NATO allies. Increases in the defense burdens of individual NATO states are distinct from their individual contributions to NATO as an organization, and arguably serve to better capture the latent power and capabilities of the NATO alliance. Ultimately, assessing the contributions of NATO members requires us to take stock of a number of such considerations as the US gains considerable flexibility from its membership in NATO and its maintenance of overseas bases and deployments. This point also carries over into other alliance relationships. For example, recently US military officials have noted that keeping troops stationed in South Korea, specifically, is cheaper than stationing those troops in the US, due to the contributions made by the South Korean government.

The takeaway

The US military presence overseas has been one of the most enduring elements of post-war foreign policy. However, our understanding of how these deployments shape the foreign policies of host-states is only now coming together. The deployment of US military personnel affects not just the host-state, but countries in that state’s neighboring region, in a variety of ways. Our study underscores the fact that these deployments have mutually reinforcing effects that lead host-states to reduce their military spending. Essentially, the US military can serve to curb higher levels of military spending than we might otherwise expect to see in a given region. It is possible that such deployments have effects that extend beyond defense spending, such as helping to curb conflict around the globe. If so, whatever the US saves by reducing its overseas military footprint may be more than offset by the costs associated with higher levels of conflict, lost trade, and generally greater instability around the globe.

[1] See the full version of the paper for full citations.

About Michael Flynn

Michael Flynn is an associate professor in the Department of Political Science at Kansas State University. He received his Ph.D. in Political Science from Binghamton University in 2013. His research focuses on the political and economic determinants of foreign economic and security policy, security issues, and state repression.

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