Introduction

The North Atlantic Treaty Organization's (NATO's) 2024 summit, marking the alliance's 75^th anniversary, is scheduled to be held in Washington, DC, July 9-11. In addition to highlighting NATO's past achievements, heads of state and government from NATO's 32 member states are expected to address a range of security challenges currently facing the alliance. Chief among these challenges is Russia's ongoing war in Ukraine. NATO officials have outlined the following key priorities for the summit:

• Enhancing NATO's collective defense and deterrence in response to security threats posed by Russia.
• Increasing allied defense spending and investment.
• Strengthening NATO support for Ukraine, including through a new NATO mission to coordinate allied security assistance and military training, and by providing a more clearly defined pathway to NATO membership.
• Enhancing relations with partners in the Indo-Pacific region, chiefly to address security threats posed by the People's Republic of China (PRC, or China).

The Washington, DC Summit (hereinafter referred to as the Washington Summit) is set to be the first NATO summit with both Finland and Sweden as members. Sweden joined the alliance in 2024 and Finland in 2023. U.S. and NATO officials assert that the addition of the two mature democracies with advanced militaries will enhance Euro-Atlantic security and strengthen NATO's defense posture, particularly in the Baltic Sea region.¹

The allies also are expected to confirm NATO's next Secretary General, outgoing Dutch Prime Minister Mark Rutte. Rutte is to replace Jens Stoltenberg, who has served in the role since 2014, and whose current mandate runs through September 30, 2024.²

The United States was the driving proponent of NATO's creation in 1949 and has been the unrivaled leader of the alliance as it has evolved from a collective defense organization of 12 members focused on deterring the Soviet Union to a globally engaged security organization of 32 members (see Figure 1). Historically, U.S. presidential administrations have viewed U.S. leadership of NATO as a cornerstone of national security policy that brings benefits ranging from peace and stability in Europe to the political and military support of important allies, including some of the world's most advanced militaries.³

Although some Members of Congress have criticized specific developments within NATO—regarding burden-sharing, for example—Congress as a whole has demonstrated consistent support for NATO and U.S. leadership of the alliance since NATO's inception.⁴ During the Trump Administration, congressional support was at times viewed by some as an effort to reassure allies troubled by former President Donald Trump's criticisms of the alliance.⁵ Since Russia's 2022 invasion of Ukraine, both chambers of Congress have passed legislation expressing support for U.S. contributions to NATO's enhanced collective defense posture and U.S. and allied assistance to Ukraine (see "Issues for Congress"). Nevertheless, some analysts caution that disagreements between the United States and its allies could emerge in several key areas, including on NATO's longer-term relations with Ukraine, how best to address threats posed by China, and on long-standing concerns about defense spending and burden-sharing. Furthermore, some allies may question U.S. credibility as a leader and ally in light of critical rhetoric about the alliance from the Trump Administration and concerns about U.S. political dynamics and foreign policy trends under future administrations.

Figure 1. NATO Members and Dates of Accession

Source: Created by CRS.

Collective Defense and Deterrence

NATO leaders have characterized Russia's 2022 full-scale invasion of Ukraine as the "most dangerous moment in European security in a generation" and have reoriented the alliance's strategic focus and defense posture to respond to the heightened security threat.⁶ NATO's most recent Strategic Concept, adopted at the July 2022 Madrid Summit, identifies Russia as "the most significant and direct threat to Allies' security and to peace and stability in the Euro-Atlantic area."⁷ The allies have echoed these concerns at subsequent meetings.

At the Washington Summit, allied leaders are expected to highlight a renewed commitment to collective defense and deterrence, including through implementation of "the most comprehensive [NATO] defense plans since the Cold War."⁸ NATO's new regional defense plans and corresponding force structure requirements—deemed by NATO to be "a larger, more demanding" request of members than NATO has made in more than three decades—specify what is expected of each ally to defend and deter "against any aggressor from any direction."⁹ NATO leaders note, however, that implementation will require increased defense investments from NATO members.¹⁰ NATO Secretary General Stoltenberg has signaled that in Washington, DC, the allies could announce new initiatives, including a Defense Industrial Pledge, intended to spur such investment. A key priority is to address shortfalls in ammunition, air and missile defense, and long-range weapons (see "Defense Spending and Investment" below).¹¹

NATO's Supreme Allied Commander Europe (SACEUR), U.S. General Christopher Cavoli, has said that implementing NATO's defense plans means "making sure we have the force commitments, command and control arrangements, and the enablement our plans require."¹² NATO leaders highlight several related milestones reached in 2024. They report that approximately 500,000 allied troops, across all domains, are currently available at high readiness, exceeding the goal of 300,000 set at NATO's 2022 Madrid Summit.¹³ In the first half of 2024, many of these forces participated in NATO's largest military operation since 1988, Operation Steadfast Defender 2024. The exercise, held between January and May 2024, involved approximately 90,000 forces from all 32 allies and demonstrated NATO's ability to deploy forces rapidly from across the alliance, including from North America, to reinforce the defense of Europe.¹⁴

NATO's new collective defense plans and force requirements are intended to bolster an enhanced NATO force posture in the eastern part of the alliance. NATO deployed to the region for the first time in the alliance's history after Russia's 2014 invasion of Ukraine. Since the February 2022 invasion, NATO has doubled the number of battalion-sized multinational battlegroups (between 1,000 and 2,000 soldiers each) along its eastern flank, deploying battlegroups in Bulgaria, Hungary, Romania, and Slovakia, in addition to the four that have been present in Estonia, Latvia, Lithuania, and Poland since 2016. A total of about 10,000 allied soldiers are deployed to the battlegroups, each led by a different "framework nation."¹⁵ Individual allies have designated combat-ready national military units to "scale-up" the battlegroups to brigade-sized units on short notice. In addition to frequent training with the battlegroups, allies have prepositioned equipment, including heavy weaponry, and established new command and control capabilities to enable rapid reinforcement when necessary.

Despite these measures, NATO members remain concerned about the potential for a wider conflict involving Russia. Leaders in the Baltic states, for example, have called for NATO to move from its "tripwire" posture, aimed at deterring a Russian military invasion, to a "forward defense posture" intended to drive back an invasion. As part of such efforts, Germany is planning to station a brigade of 4,800 personnel in Lithuania by 2027,¹⁶ and Canada and Latvia have signed a plan for scaling up the NATO battlegroup in Latvia to brigade size, including the persistent deployment of 2,200 Canadian personnel, by 2026.¹⁷

Defense Spending and Investment

Russia's war in Ukraine has added urgency to longer-standing NATO efforts to increase allied defense spending and investment. Following Russia's 2014 illegal annexation of Crimea and invasion of Ukraine, the allies adopted the so-called Wales Defense Investment Pledge, under which they committed to "aim to move towards" adopting national defense budgets that meet or exceed 2% of GDP and devote at least 20% of defense spending to procurement and modernization by the year 2024.²⁰

NATO officials report some progress toward these goals. According to NATO, 2024 marked the tenth consecutive year of increased defense spending by European allies and Canada, with a cumulative investment totaling at least $640 billion in additional defense spending since 2014. NATO estimates that 23 allies are meeting the 2% of GDP benchmark in 2024, compared with 3 in 2014 (see Figure 2), and 29 NATO allies are meeting the 20% procurement and modernization target.²¹

At NATO's 2023 Vilnius Summit, allies strengthened their commitment to NATO's defense spending guidelines, stressing that 2% of GDP be seen as a minimal spending requirement and that "in many cases, expenditure beyond 2% of GDP will be needed."²² Some analysts noted that the Vilnius defense spending language fell short of more ambitious spending targets reportedly advocated by some allies—including the United States, UK, and Poland—before the summit, possibly reflecting a reluctance by some allies facing continued economic challenges related to inflation and the war in Ukraine.²³

Figure 2. Progress on Meeting NATO's 2% of GDP Defense Spending Guideline Defense Expenditure as a Percentage of GDP, 2014 and 2024 (estimated)

Source: Figure created by CRS based on data from NATO, "Defense Expenditures of NATO Countries," June 17, 2024. Note: The figure does not include NATO ally Iceland, which does not have armed forces.

Since Russia's February 2022 invasion of Ukraine, most allied governments have increased their respective national defense budgets. In particular, several major European countries, including Germany and France, have pledged to significantly bolster defense spending. For example, noting that Europe is now in a "war economy," French President Emmanuel Macron has proposed a 40% increase in defense spending for the next budget cycle (2024-2030).²⁴ In Germany, Chancellor Olaf Scholz announced in February 2022 a historic turning point (Zeitenwende) in German defense policy, including plans to establish a new €100 billion (about $110 billion) special defense fund—more than double the size of Germany's 2021 defense budget (€47 billion, or about $52 billion)—to be used for investment and armaments projects, including acquisition of U.S.-made F-35 fighter jets capable of carrying nuclear weapons. In addition to the one-time defense modernization fund, Scholz also said that he would henceforth propose annual defense budgets exceeding 2% of GDP. In 2022, the Polish parliament passed a law mandating that annual defense spending should equal at least 3% of GDP.²⁵

U.S. and NATO officials have welcomed the renewed commitment to meet NATO defense spending goals, especially after economic challenges connected to the COVID-19 pandemic appeared to slow defense spending across the alliance in 2021 and early 2022. At the same time, some analysts caution that the war in Ukraine could expose long-standing shortfalls in European military capacity.²⁶ NATO officials have expressed particular concern about low munitions stockpiles in most member states, and reportedly have assessed that allies are currently able to provide no more than 5% of the air defense capabilities deemed necessary to defend allies in Central and Eastern Europe from a full-scale attack.²⁷

Some European governments have begun to contract with the defense sector to ramp up munitions production, but analysts and industry representatives caution that it could take time to develop the necessary manufacturing capacity, leaving a potential short-term gap between Ukraine's defense needs and European supply.²⁸ The supply shortfalls have led to renewed calls for more pan-European coordination to produce arms and supply Ukraine. Proponents of greater European defense cooperation, including the joint production and acquisition of needed capabilities, argue that coordination can create important budgetary efficiencies and further stretch limited resources.

Some progress toward greater intra-European coordination has been made, both within the 27-member European Union (EU) and at NATO (23 NATO allies also belong to the EU). In March 2023, for example, EU leaders announced a plan to supply Ukraine with 1 million 155-millimeter artillery shells by the end of March 2024 (either from existing stocks or through joint procurement) and to replenish EU stocks and ramp up production.²⁹ The EU reportedly fell short of its initial target for Ukraine (with EU officials estimating that just over 500,000 shells were delivered to Ukraine by March 2024), but EU officials say that production capacity in the EU has increased by between 20% and 30% and have pledged to send 1.1 million shells to Ukraine by the end of 2024.³⁰

In January 2024, NATO Secretary General Stoltenberg announced that the NATO Support and Procurement Agency (NSPA) would help coordinate the purchase of up to 1,000 Patriot missiles by a coalition of NATO allies including Germany, the Netherlands, Romania, and Spain. The $5.5 billion contract, awarded to a joint venture between Raytheon and German company MBDA, is also intended to support the development of additional European production capacity.³¹ Also in January, Secretary General Stoltenberg announced that the NSPA had concluded contracts for the purchase of 220,000 rounds of 155-millimeter artillery shells to replenish allies' stocks.³²

In 2022, the German government announced that it would partner with 15 allies to jointly procure air defense systems for short-, medium-, and long-range defense under a new European Sky Shield Initiative.³³ The government consortium is reportedly considering purchase of German or Israeli systems as well as U.S.-made Patriot systems; it has decided against a Franco-Italian-manufactured system favored by Italy and France.³⁴ This decision reportedly contributed to French and Italian government opposition to the initiative and reignited criticism that the European defense industry remains fractured and compartmentalized along national lines, with national governments often remaining more committed to protecting domestic constituencies than making substantive progress in joint capabilities development.³⁵ More broadly, some critics warn that certain governments, including Germany, could face challenges in developing the institutional capacity and procurement mechanisms to efficiently allocate substantial new defense funding.³⁶

NATO Support for Ukraine

A key summit priority for NATO officials is to institutionalize long-term allied support for Ukraine, both from individual allies and from NATO as a whole. Secretary General Stoltenberg has outlined three main deliverables in this regard: (1) a new NATO leadership role in coordinating security assistance and training for the Ukrainian Armed Forces; (2) a multiyear financial pledge of support from NATO allies; and (3) advancing Ukraine's path to NATO membership.³⁷

At the summit, allies are expected to endorse a proposal for NATO to lead coordination of allied security assistance for Ukraine. Under the proposal, agreed by NATO defense ministers in June 2024, assistance from individual NATO members would be coordinated by a NATO command, located at a U.S. Army facility in Wiesbaden, Germany, and logistical nodes in the eastern part of the alliance; the coordination effort would involve close to 700 personnel from NATO and partner countries, under the command of the SACEUR. NATO would also oversee training of Ukrainian armed forces at facilities in NATO member states.³⁸

Although NATO has played an increasingly proactive role in coordinating security assistance to Ukraine, the United States has thus far convened and led international coordination efforts, including through the Ukraine Defense Contact Group, also known as the "Ramstein format" (after the U.S. military base in Germany where the Contact Group typically meets). Secretary General Stoltenberg and a number of allied governments have called for NATO to take on more responsibility for coordinating assistance from NATO allies. Stoltenberg argues that anchoring allied support for Ukraine in a "robust NATO framework," and relying less on "voluntary contributions" and "short-term offers" and more on "NATO commitments" and "multi-year pledges," could ensure more reliable and predictable security assistance over the long term. Arguing that NATO allies account for 99% of all security assistance to Ukraine, he has asserted that an enhanced NATO role also could "make [allied] efforts more efficient, and effective."³⁹

Press reports ahead of the Washington Summit suggest that the new NATO initiative to coordinate security assistance and training would replace efforts currently carried out by the International Donor Coordination Center (IDCC), led by the United States in cooperation with the UK, and the Security Assistance Group-Ukraine (SAG-U), under which the United States and Canada have coordinated training efforts for Ukrainian forces. The new NATO effort reportedly would run in parallel with the U.S.-led Contact Group, which also includes almost 20 non-NATO members.⁴⁰

In Washington, DC, NATO allies are also expected to announce a collective multiyear pledge of allied security assistance for Ukraine. The total amount of such a commitment, and the extent to which allies are willing to pledge beyond what they have already committed, remains unclear (see the text box below for information on European assistance to Ukraine). According to press reports, allies did not reach consensus on an April 2024 proposal by Stoltenberg for $100 billion in additional assistance to Ukraine to be coordinated by NATO. Some observers speculate that the allies could instead pledge at the summit to maintain current or more moderately increased assistance levels over the next five years or beyond, again stressing that NATO would coordinate spending priorities.⁴¹

Some analysts have characterized the efforts to secure longer-term pledges of assistance and institutionalize NATO coordination as a response to unpredictable political dynamics in some member states with respect to supporting Ukraine. They point specifically to political debates and related delays in assistance in some member states, including the United States.⁴²

A key question for NATO remains whether and how to offer Ukraine a clearer path to membership. Since 2008, NATO has reiterated a broad pledge that Ukraine will one day become a member but has not offered a timetable of specific benchmarks for a formal invitation. The Biden Administration and some other allied governments have said Ukraine will not join NATO while the war is ongoing.⁴⁶ Other allies, including Poland and the Baltic states, have called for a more defined pathway to membership and have cautioned that postponing membership decisions could incentivize Russia to prolong the war.⁴⁷

At NATO's 2023 summit in Vilnius, Lithuania, allies declared that "Ukraine's future is in NATO," and pledged to work closely with Ukraine to enact the reforms necessary for NATO membership.⁴⁸ They also announced that Ukraine had "moved beyond" the need for a Membership Action Plan, typically required for aspiring members.⁴⁹ The allies continue to debate proposals from some NATO members to open formal accession talks with Ukraine, with the understanding that membership would not be finalized until the end of the war. Observers caution, however, that the Biden Administration and a number of allied governments remain reluctant to advance Ukraine's membership under current conditions.⁵⁰

Security Threats from China and Partnerships in the Indo-Pacific Region

NATO and U.S. officials have stressed the importance of strengthening NATO's relationships with partners outside the Euro-Atlantic area, and particularly in the Indo-Pacific region. Since 2021, when NATO for the first time outlined "systemic challenges" posed by China's "assertive behavior" and "coercive policies which stand in contrast to the fundamental values enshrined in [NATO's founding treaty]," the allies have moved to enhance cooperation with partners in the Indo-Pacific.⁵¹ Secretary General Stoltenberg and U.S. Secretary of State Antony Blinken have argued that China's and North Korea's support for Russia's war in Ukraine underscores the importance of these efforts.⁵² The leaders of NATO's four main Indo-Pacific partners—Australia, Japan, New Zealand, and South Korea—are expected to attend the Washington Summit (they also participated in NATO's 2022 and 2023 summits).

NATO's agreement to identify PRC activities that could threaten allied security followed several years of calls from the Biden and Trump Administrations and some Members of Congress who have urged NATO to assess the security implications of growing Chinese investment in Europe and to more proactively counter potential negative impacts on transatlantic security.⁵³ U.S. officials have expressed particular concern about Chinese investment in critical infrastructure and telecommunications systems, such as 5G networks. NATO has also strengthened resilience guidelines for member states, including for critical infrastructure and supply chains and for maintaining NATO's technological edge.

Despite growing consensus within the alliance on security challenges posed by China, some analysts have noted that certain European governments remain reluctant to antagonize a major economic partner and appear to worry about the broader implications of a more confrontational relationship with Beijing.⁵⁴ The allies also remain divided on how to respond to PRC assertiveness. In an April 2023 press interview following a visit to China, French President Macron commented that Europe should reduce its dependency on the United States and avoid getting involved in a U.S.-China confrontation over Taiwan.⁵⁵ Ahead of the 2023 Vilnius Summit, Macron reportedly opposed a Stoltenberg-backed proposal to open a NATO office in Japan. Macron previously stressed that the alliance faced more significant security challenges in the North Atlantic region than from China.⁵⁶

Officials from several allied governments, including Poland, the United States, and the UK, criticized Macron's statements with respect to China and Taiwan.⁵⁷ More recent statements by the EU and NATO also reflect a growing consensus within the alliance that NATO must address the wide-ranging security implications posed by China's growing economic, military, and political influence, including with respect to the war in Ukraine.⁵⁸

Issues for Congress

Congress was instrumental in creating NATO in 1949—including through Senate ratification of NATO's founding North Atlantic Treaty—and has played a role in shaping U.S. policy toward the alliance ever since. Although some Members of Congress have criticized specific developments within NATO—regarding the extent of allied burden-sharing, for example—Congress as a whole has consistently demonstrated support for NATO and its cornerstone mutual defense commitment, articulated in Article 5 of the North Atlantic Treaty. This support has manifested through an array of congressional actions, including financial support through the authorization and appropriations processes, Senate ratification of nine rounds of NATO enlargement, and endorsement of U.S. participation in NATO military operations and defense and deterrence efforts. Many in Congress have also often called on U.S. presidential administrations to do more to secure increased allied commitments to NATO and more allied defense spending.⁵⁹

At NATO's 2024 Washington Summit, allied leaders are expected to engage on a number of issues of potential interest to Congress, ranging from NATO's evolution over its 75-year history to key security and defense issues currently facing the alliance. Issues of particular interest to Congress may include the following:

• The future of NATO and U.S. Force Posture in Europe. NATO has reoriented its collective defense posture in Europe to respond to the threat from Russia. Key questions remain, however, about the longer-term sustainability of these efforts, whether the alliance's current force posture would be adequate to deter or defend against a possible Russian military attack, and the U.S. role in such a response.
• NATO Support for Ukraine. While some in Congress have voiced support for Ukraine's NATO membership aspirations and a majority have voted in favor of U.S. bilateral assistance to Ukraine, others have expressed opposition.⁶⁰ Ukraine's membership prospects and a more robust NATO role in coordinating security assistance to Ukraine could factor into congressional consideration of potential longer-term support for Ukraine.
• Allied Defense Spending. Throughout NATO's history, Congress has urged European allies and Canada to increase defense spending. Some Members have suggested that allied defense spending levels could influence congressional deliberations over potential future U.S. security commitments in Europe.⁶¹
• China. As Congress pursues policy responses to strategic competition with and security threats from China, Members may seek to engage with NATO and its member states in developing NATO strategy toward China and shaping broader alliance policy in the Indo-Pacific region. The security ramifications of China's investment in Europe could be a particular concern.

More broadly, Members of Congress could consider a range of questions related to U.S. leadership of the alliance, including with respect to future U.S. commitments to NATO and European security, allied perceptions of U.S. leadership of NATO, and the costs and benefits of U.S. membership in NATO. Congressional consideration of these issues increased during the Administration of former President Donald Trump, whose criticisms of the alliance and assertions that NATO is a "bad deal" for the United States prompted debate among some analysts and policymakers about the benefits to the United States of its leadership of the alliance.⁶²

During and following the Trump Administration, both chambers of Congress passed legislation expressing support for NATO; some Members portrayed such measures as efforts to rebut Trump and other NATO critics.⁶³ Section 1250A of the FY2024 National Defense Authorization Act (P.L. 118-31), for example, states that "the President shall not suspend, terminate, denounce, or withdraw the United States from [NATO] ... except by and with the advice and consent of the Senate" and prohibits the use of government funds for such purposes. On the other hand, some Members of Congress have continued to question the value of the United States' historically robust role in European security matters and have credited former President Trump's approach to NATO with securing defense spending increases across the alliance that were not forthcoming under his predecessors.⁶⁴