The Law of War and the Russian Invasion of Ukraine

"In the days after Russia’s invasion of Ukraine on February 24, 2022, many countries condemned the action as a violation of international law governing when countries may use force against one another. Since then, several observers, including the U.S. Secretary of State and other foreign government officials, have cited evidence that the Russian military has targeted civilians, struck protected sites, and taken other actions that violate international law regulating the conduct of war. This Legal Sidebar provides a brief introduction to the international legal framework governing the use of force in the invasion of Ukraine and concludes with a discussion of avenues for accountability and options for Congress.

Terminology

The law of war generally refers to the portion of international law that regulates the inception of use of force, the conduct of hostilities, and the protection of war victims, among other things. The term is often used interchangeably with the law of armed conflict and international humanitarian law. There are two major categories under the law of war umbrella: jus ad bellum (legal rules governing when a country can resort to use of force) and jus in bello (law governing conduct during the use of force). While they can be interrelated, jus ad bellum and jus in bello generally operate independently such that compliance with one category is required regardless of compliance with the other. For example, a state that is a victim of a jus ad bellum violation because it is attacked without a lawful basis must still comply with jus in bello when conducting military operations to defend itself.

Jus ad Bellum: Deconstructing the Justifications for War in Ukraine

The starting point to analyze most aspects of jus ad bellum is the U.N. Charter. Article 2(4) prohibits member-states from using or threatening to use force against one another, but there are exceptions. Article 51 preserves member-states’ right to act in either individual or collective self-defense when an armed attack occurs, and Chapter VII of the charter permits the U.N. Security Council to authorize military actions necessary to maintain or restore international peace and security. A state can also consent to the use of force in its territory. 

Customary international law (described in this CRS Report) also informs jus ad bellum. Customary international law requires that the use of force be proportionate to the justification for military action and necessary because no other reasonable means of redress are available..."
Law of War and Russia 

Russia’s Nuclear Weapons: Doctrine, Forces, and Modernization

"Russia’s nuclear forces consist of both long-range, strategic systems—including intercontinental ballistic missiles (ICBMs), submarine-launched ballistic missiles (SLBMs), and heavy bombers—and shorter- and medium-range delivery systems. Russia is modernizing its nuclear forces, replacing Soviet-era systems with new missiles, submarines and aircraft while developing new types of delivery systems. Although Russia’s number of nuclear weapons has declined sharply since the end of Cold War, it retains a stockpile of thousands of warheads, with more than 1,500 warheads deployed on missiles and bombers capable of reaching U.S. territory.

Doctrine and Deployment

During the Cold War, the Soviet Union valued nuclear weapons for both their political and military attributes. While Moscow pledged that it would not be the first to use nuclear weapons in a conflict, many analysts and scholars believed the Soviet Union integrated nuclear weapons into its warfighting plans. After the Cold War, Russia did not retain the Soviet “no first use” policy, and it has revised its nuclear doctrine several times to respond to concerns about its security environment and the capabilities of its conventional forces. When combined with military exercises and Russian officials’ public statements, this evolving doctrine seems to indicate that Russia has potentially placed a greater reliance on nuclear weapons and may threaten to use them during regional conflicts. This doctrine has led some U.S. analysts to conclude that Russia has adopted an “escalate to de-escalate” strategy, where it might threaten to use nuclear weapons if it were losing a conflict with a NATO member, in an effort to convince the United States and its NATO allies to withdraw from the conflict. Russian officials, along with some scholars and observers in the United States and Europe, dispute this interpretation; however, concerns about this doctrine have informed recommendations for changes in the U.S. nuclear posture.

Russia’s current modernization cycle for its nuclear forces began in the early 2000s and is likely to conclude in the 2020s. In addition, in March 2018, Russian President Vladimir Putin announced that Russia was developing new types of nuclear systems. While some see these weapons as a Russian attempt to achieve a measure of superiority over the United States, others note that they likely represent a Russian response to concerns about emerging U.S. missile defense capabilities. These new Russian systems include, among others, a heavy ICBM with the ability to carry multiple warheads, a hypersonic glide vehicle, an autonomous underwater vehicle, and a nuclear-powered cruise missile. The hypersonic glide vehicle, carried on an existing long-range ballistic missile, entered service in late 2019.

Arms Control Agreements

Over the years, the United States has signed bilateral arms control agreements with the Soviet Union and then Russia that have limited and reduced the number of warheads carried on their nuclear delivery systems. Early agreements did little to reduce the size of Soviet forces, as the Soviet Union developed and deployed missiles with multiple warheads. However, the 1991 Strategic Arms Reduction Treaty, combined with financial difficulties that slowed Russia’s nuclear modernization plans, sharply reduced the number of deployed warheads in the Russian force. The 2010 New START Treaty added modest reductions to this record but still served to limit the size of the Russian force and maintain the transparency afforded by the monitoring and verification provisions in the treaty.

Congressional Interest

Some Members of Congress have expressed growing concerns about the challenges Russia poses to the United States and its allies. In this context, Members of Congress may address a number of questions about Russian nuclear forces as they debate the U.S. nuclear force structure and plans for U.S. nuclear modernization. Congress may review debates about whether the U.S. modernization programs are needed to maintain the U.S. nuclear deterrent, or whether such programs may fuel an arms race with Russia. Congress may also assess whether Russia will be able to expand its forces in ways that threaten U.S. security if the United States and Russia do not continue to limit their forces under the New START Treaty. Finally, Congress may review the debates within the expert community about Russian nuclear doctrine when deciding whether the United States needs to develop new capabilities to deter Russian use of nuclear weapons..."
Russia's nuclear weapons 

Russia’s Invasion of Ukraine: Overview of U.S. and Allied Responses

"Russia launched a full-scale air, land, and sea attack on the independent and democratic state of Ukraine on February 24, 2022. The United States and its allies around the world have condemned Russia’s “unprecedented military aggression” as “unprovoked and unjustified.” On February 24, President Biden said,

"Now the entire world sees clearly what [Vladimir] Putin and his Kremlin allies are really all about. This was never about genuine security concerns.... It was always about naked aggression, about Putin’s desire for empire by any means necessary—by bullying Russia’s neighbors through coercion and corruption, by changing borders by force, and, ultimately, by choosing a war without a cause. Putin’s actions betray his sinister vision for the future of our world—one where nations take what they want by force."

Moscow’s objectives appear to include a broad seizure of territory across Ukraine and replacement of Ukraine’s democratically elected government with a nondemocratic satellite regime. Russia also may be seeking to annex a greater part of eastern and southern Ukraine, leaving a rump Ukraine to serve as a puppet state. Reports show many incidents of Ukrainian armed forces’ resistance to the Russian invasion. Many civilians have fled their homes, and Ukraine’s government has ordered a general military mobilization. Russian troops reportedly entered Ukraine’s capital, Kyiv, on February 25, 2022.

Since December 2021, the United States and allies had warned Russian officials they were prepared to impose severe new sanctions on Russia if it launched a new invasion of Ukraine, a country Russia first invaded and partially occupied in 2014. The United States and allies imposed an initial round of sanctions on February 21-23, 2022, in response to Russia’s purported recognition of two Russia-occupied regions in eastern Ukraine as independent states. The United States and allies imposed more sanctions on February 24, 2022, after Russia launched its attack. Members of Congress are considering additional sanctions on Russia and other actions in response to Russia’s invasion of Ukraine..."
Russia's invasion Ukraine 

Russia: Background and U.S. Interests

"Since 1991, Congress has played a key role in the development of U.S. policy toward the Russian Federation (Russia), the principal successor to the United States’ former superpower rival, the Soviet Union. In that time, U.S.-Russian relations have gone through positive and negative periods. Each new U.S. Administration has sought to improve U.S.-Russian relations at the start of its tenure, and the Donald J. Trump Administration has expressed similar intentions to rebuild constructive relations with Moscow. In doing so, however, the Administration has indicated it intends to adhere to core international commitments and principles, including retention of sanctions against Russia. Moving forward, the 115th Congress is expected to actively engage with the Administration on questions concerning U.S.-Russian relations..."
Russia