The Pentagon's Review of U.S. Forces in Europe and the Outlook for NATO's Security Architecture

Executive Summary

The Pentagon has accelerated its Europe Posture Review, originally scheduled for December, directing that at least four reduction options be drafted by November 6. The criteria for these reductions are being designed to extend beyond the existing equity principle of total defense spending to include factors such as guarantees for base and airspace access and the degree of cooperation with the United States, including on issues like the war in Iran. This is the result of a combination of two factors: the Trump administration's National Defense Strategy logic of reallocating resources to prioritize the Indo-Pacific, and President Trump's personal view of alliances, which seeks to tie the scale of reductions to individual countries' political compliance. The preemptive response from countries like Hungary and Romania, which have offered targeted contributions such as sharing base operating costs, shows that differentiated reductions based on this "cooperation" criterion are already being accepted as a fait accompli. The most probable path forward is differentiated reductions for each country based on their level of cooperation. This risks transforming NATO into an alliance structure governed by political relationships rather than budget negotiations. South Korea must closely watch this precedent, as it could lead to a shift in the standards for its own Special Measures Agreement (SMA) negotiations and discussions on extended deterrence.

I. Situational Analysis of the Issue

The Pentagon's Review of U.S. Forces in Europe: A Situational Analysis

1. Background and Developments

The starting point for this review is the National Defense Strategy (NDS) released in early December of last year by the second Trump administration. This strategy codified the assessment that the United States lacks the financial and industrial capacity to respond simultaneously to threats in multiple regions [6]. A key implementation measure presented was the demand that allies increase their share of the burden for their own defense [2].

Immediately after taking office, Secretary of Defense Hegseth traveled to Brussels to personally convey this policy direction. He stated that Europe must take "ownership of the continent's conventional security" [4]. This past June, he announced that some U.S. military assets would be withdrawn from the NATO Force Model. This signaled the U.S. position that it would no longer serve as the primary guarantor of European security in the event of a full-scale conventional war with Russia [4][6].

The current Europe Posture Review is the process of putting this announcement into the implementation phase. It was formalized this June with an original target completion date of December [4]. However, according to a document obtained by Reuters, the deadline for submitting draft proposals of at least four reduction options to Secretary Hegseth has been moved up to November 6 [1][3].

2. Current Situation

According to Defense News, the review is proceeding at an unusually rapid pace, with options being drafted by early November, well ahead of the final December deadline [1]. The discussion within the United States is already being framed as "Leave Europe to the Europeans." Foreign Affairs assesses that since Hegseth's remarks in Brussels, this policy has entered the implementation stage [4].

EAI analysis reveals that the criteria for troop redeployment are not limited to total defense spending. The level of guarantees for base and airspace access and the degree of cooperation with U.S. foreign policy, such as on the war in Iran, will also be factored in [3]. Foreign press reports citing the document obtained by Reuters convey concerns that countries Trump judged as not supporting the U.S. during the Iran-Israel war could be targeted for reductions [3]. This means that, unlike the existing equity standard of defense burden-sharing (spending as a percentage of GDP), the political cooperation of individual countries could determine the scale of reductions.

There are signs that some Eastern European countries have already taken preemptive action. Countries like Hungary and Romania have offered the targeted contribution of sharing base operating costs instead of increasing their total defense budgets [3]. This suggests that the substance of the "proof of cooperation" demanded by the U.S. is not the total budget amount but concrete actions to alleviate the American burden [3].

Changes are also already being detected at the operational level. The U.S. Army has decided to terminate the operations of an experimental drone battalion in Europe after less than a year [15]. The dismissal of the commanding general of the U.S. Army's V Corps in Europe is also cited as an example of friction in the readjustment process [6]. However, it is currently unclear whether this was a measure directly linked to the Europe Posture Review or a separate personnel and organizational management issue.

Meanwhile, the internal situation at the U.S. Department of Defense could also be a variable affecting the direction of this review. Secretary of the Army Driscoll reportedly resigned amid rumors of conflict with Secretary Hegseth, a report the White House has not denied [10][16]. There are also reports that the Office of the Secretary of Defense has created friction with congressional oversight functions by deleting a public report on weapons testing results [11]. Speculation has also arisen about Secretary Hegseth's personal political standing; President Trump commented on rumors of a 2028 presidential run by saying it was "still early" but that Hegseth was "doing a great job" [7]. Such internal personnel conflicts and the weakening of oversight functions at the Pentagon are factors that add uncertainty to the policy consistency of the Europe Posture Review.

3. Key Actors and Positions

U.S. Department of Defense (Secretary Hegseth): The implementing body applying the National Defense Strategy's principle of reallocating resources to prioritize the Indo-Pacific. Its position is to base reduction criteria not on total defense spending but on cooperation with foreign policy and guarantees for base and airspace access [1][3]. However, it remains to be seen whether the momentum for this policy will be consistently maintained, as the department is simultaneously experiencing organizational turmoil, including the resignation of the Secretary of the Army and controversy over the deletion of an oversight report [10][11].

President Trump: The political source of the "Leave Europe to the Europeans" policy. He employs a strategy of using security commitments as bargaining chips with allies, as demonstrated by his pressure on the UK to increase defense spending and his remarks about reconsidering the Falkland Islands issue [12]. The domestic political calendar, with the November midterm elections approaching, could affect the pace of policy implementation [7][9].

Eastern European NATO Members (e.g., Hungary, Romania): Have opted for a targeted response of sharing base operating costs instead of operating within the existing framework of increasing total defense spending. This shows that these countries have discerned that the real criterion for reductions is not the total budget amount but specific cooperative actions [3].

Major Western European Countries and the NATO Secretariat: The epicenter of growing concerns about the collapse of equity and selective, differentiated reductions. Concerns are being raised that if cooperation with foreign policy is factored in addition to defense spending, countries that differed from the U.S. on specific issues like the war in Iran could be penalized [3].

U.S. Congress: A check on executive power, holding the power of the purse. It is cited as a source of caution that could put the brakes on a rapid withdrawal of troops [3]. As seen in the backlash from Senator Warren and others over the Pentagon's deletion of a weapons test report, the conflict between the executive branch and Congress over oversight functions could also spill over into a transparency issue for this review [11].

4. Key Issues

The first issue is the nature of the reduction criteria. The center of gravity is shifting from the quantitative standard of defense spending to the qualitative and political standard of cooperation with foreign policy [3]. This is a change that could alter the nature of burden-sharing discussions throughout the entire system of alliances and multilateral security.

The second is the issue of pace and sequence. The decision to move up the deadline for submitting options to November 6, ahead of the official December completion date, reflects the Trump administration's determination to push the policy forward [1]. However, the actual pace of implementation remains fluid due to the simultaneous presence of constraining factors such as congressional budgetary power, backlash from European countries, and internal personnel conflicts at the Pentagon [3][10].

The third is the variable of U.S. domestic politics. The November midterm elections, Secretary Hegseth's political future, and internal leadership conflicts at the Pentagon are identified as factors that could affect the policy's consistency and sustainability [7][9][10].

The fourth is the linkage with the regional situation. As the reduction of the U.S. role as the primary guarantor of European security was announced while the Russia-Ukraine war continues, the direction of end-of-war negotiations and the pace of European rearmament will likely be key variables determining the scale of the final U.S. force redeployment plan [4][6].

II. In-Depth Analysis of the Issue

The Pentagon's Review of U.S. Forces in Europe: An In-Depth Analysis

1. Root Cause: The Clash Between Fiscal/Industrial Constraints and Indo-Pacific Priorities

The roots of this review lie not in budget documents but in the National Defense Strategy. The second Trump administration's NDS explicitly stated that the United States does not have the fiscal and industrial capacity to respond to threats in multiple theaters simultaneously [6]. This is not mere rhetoric but a real constraint on the allocation of the defense budget. The Brookings Institution summarizes this logic with the proposition that "simultaneous threats are real, and the United States cannot bear the entire burden alone" [2]. This is followed by the demand that allies must spend more, deploy more forces, and take greater responsibility in their own regions [2].

The problem is that this constraint does not apply only to Europe. Considering the pace of China's military buildup in the Indo-Pacific, Europe is inevitably relegated to a lower priority in Washington's calculations. Secretary Hegseth's trip to Brussels immediately after taking office to declare that "Europe must take ownership of the continent's conventional security" [4] was a result of this resource allocation priority, not its cause. In other words, the reductions in Europe were not initiated based on an assessment of the European situation but were designed as a byproduct of the higher strategic goal of reallocating resources to the Indo-Pacific region.

This is combined with Trump's personal view of alliances. He has long criticized the defense spending of NATO allies through a "free-riding" frame. The fact that the reduction criteria in this review extend beyond total defense spending to include guarantees for base and airspace access and cooperation with U.S. foreign policy [3] shows this personal calculus being institutionalized. The spread of concern within NATO that countries Trump judged as not supporting the U.S. during the Iran-Israel war could be targeted for reductions [3] is part of the same context.

2. Structural Context

Security Architecture: From a Single NATO Axis to a Dual Axis

Since the end of the Cold War, NATO has effectively operated on a single-axis structure where the U.S. provides the bulk of deterrence and Europe plays a supporting role. EAI analysis assesses that this structure is currently in a "transitional period toward a dual U.S.-Europe axis structure" [6]. The fact that the war in Ukraine is in its fifth year acts as a pressure forcing this transition. With the threat of Russian westward expansion ever-present, the U.S. declaration that it will step down as the primary guarantor in a full-scale conventional war [4] sends a message that European countries have no choice but to strengthen their own defenses.

This structural transition is not occurring uniformly. The three Baltic states are absorbing the lessons of drone warfare and experimenting with a rapid innovation model centered on defense startups [6], while major defense contractors like the UK's BAE Systems are developing unmanned combat aircraft, indicating that an industrial-level response is already underway [6]. In contrast, some Eastern European countries like Hungary and Romania are responding not by increasing their total defense spending but with the targeted measure of sharing base operating costs [3]. This shows that even within Europe, responses to U.S. pressure are diverging based on the political and economic conditions of each country.

Political Structure: Tension Between Congressional Budgetary Power and Presidential Discretion

The overseas deployment of U.S. forces falls within the president's discretionary authority as commander-in-chief, but the budget is subject to congressional approval. As EAI analysis points out, "a cautious view also coexists, suggesting that congressional budgetary power, backlash from European countries, and Trump's own political calculations could put the brakes on a rapid withdrawal" [3]. Indeed, it has been reported that even the issue of Falklands sovereignty was raised as leverage to pressure the UK on defense spending [12]. This suggests that the review of reductions is being used as a bargaining chip in bilateral negotiations with individual allies, going beyond purely military necessity calculations.

The political turmoil within the Pentagon is another variable shaking the stability of this review. The resignation of Secretary of the Army Driscoll [10][16] and the dissent expressed by four-star generals regarding the order to extend the war in Iran [14] show that the turmoil surrounding Secretary Hegseth's leadership is growing. While it is unclear to what extent these internal conflicts are affecting the pace or substance of the review's practical work, they are clearly a factor that reduces the predictability of the policymaking process.

Economic Structure: Restructuring of the Defense Industrial Supply Chain

The discussion of European self-reliance is intertwined with the issue of defense industrial supply chains. SIPRI points out that European countries are expanding research into "dual-use design" to integrate private-sector research and innovation into defense [6]. However, due to structural constraints such as vulnerable raw material supply chains and stricter export controls on dual-use technologies, it is difficult for Europe to break its dependence on the U.S. in the short term [6]. This means that even if U.S. force reductions are implemented, a gap in Europe's own deterrence capabilities is likely to persist for a considerable period.

3. Comparison with Historical Precedents

Differences from Post-Cold War Reductions

The scale of the U.S. military presence in Europe has already been significantly reduced since the end of the Cold War. Troop levels, which exceeded 300,000 in the early 1990s, were cut to tens of thousands in the 2000s. However, those reductions were based on a clear change in the security environment: the dissipation of the threat following the collapse of the Soviet Union. This review is different in nature because it is taking place in the opposite security environment, one where Russia's invasion of Ukraine and the threat of its westward advance persist. The distinctive feature of this case is that reductions are being discussed not because the threat has diminished, but because U.S. priorities are shifting to another theater.

Similarities with the Obama Administration's "Pivot to Asia"

Structurally, it shares a similar logical framework with the Obama administration's "Pivot to Asia" policy. At that time, the goal was also to reallocate resources tied up in the Middle East and Europe to the Indo-Pacific. However, whereas the Obama administration pursued a gradual reallocation of assets without shaking the core commitment to the NATO alliance, this review is far more transactional in nature, as it explicitly introduces the conditional yardstick of evaluating each country's "degree of cooperation" [3]. This reflects the Trump administration's distinctive approach of treating alliances not as communities of shared values but as individual contractual relationships.

Parallels with Discussions on Reducing U.S. Forces in Korea

From South Korea's perspective, a more direct comparison is the discussion in the early to mid-2000s on the reduction and realignment of U.S. Forces Korea (USFK), including the relocation of Yongsan Garrison and the realignment of the 2nd Infantry Division. At that time as well, negotiations for the Special Measures Agreement (SMA) and discussions on U.S. force realignment proceeded in tandem. The fact that this Europe Posture Review defines the essence of "proving cooperation" not as the total budget amount but as concrete actions to alleviate the burden [3] foreshadows that future SMA negotiations could also see the emergence of qualitative criteria beyond demands for a simple increase in the total contribution, such as base access, missile defense integration, and the level of cooperation in checking China.

4. Key Variables Shaping Future Developments

First, the specific content of the options presented on November 6. The scale of troop numbers and the regions targeted by the at-least-four reduction scenarios will determine the intensity of the equity debate among NATO members. The impact on NATO cohesion will be qualitatively different depending on whether only Eastern European countries are targeted or if core assets in Western Europe are also included.

Second, the political standing of Secretary Hegseth.Amid the resignation of the Secretary of the Army[10][16] and friction with top military leaders,[14] speculation by some about his potential 2028 presidential run[7] affects how forcefully he can push his policy agenda within the Department of Defense. President Trump’s defense of Hegseth, stating that he is doing a “fantastic job” even while noting it is “very early” to discuss a presidential campaign,[7] suggests that the Hegseth-led review will continue for the time being.

Third is the progress of negotiations to end the war between Russia and Ukraine.If negotiations to end the war succeed, or at least lead to a ceasefire, the United States will more easily find justification for troop reductions in Europe. Conversely, if the war drags on or Russia engages in further provocations, arguments for moderating the pace of reductions are likely to gain traction[3].

Fourth are the political calculations in the U.S. Congress ahead of the midterm elections.With the Republican Party seeking to maintain its majorities in both the House and Senate,[9] if troop reductions in NATO countries become a domestic political issue, the process could be blocked during congressional budget approvals. This will be a test of whether the institutional constraint of Congress’s “power of the purse,” as pointed out by EAI, will actually come into play[3].

Fifth, from the perspective of U.S.-China strategic competition, is the speed and scale at which resources and troops freed up by this review are actually redeployed to the Indo-Pacific.If the reductions in Europe merely result in budget savings rather than directly leading to a force buildup in the Indo-Pacific, it will be difficult to interpret this as a signal of strengthened security commitments to Indo-Pacific allies, including South Korea. Instead, where the tangible benefits of these reductions are directed will be a crucial reference point for the South Korean government as it designs its future strategies for the Nuclear Consultative Group (NCG) and Special Measures Agreement (SMA) negotiations.