I'll examine the legal arguments and stated justifications on both sides of this question.
Whether Russia's invasion of Ukraine is justified depends on the legal and political framework used to evaluate it. Russia and the majority of the international community offer sharply different assessments.
Russia's Stated Justifications
Moscow framed the February 2022 full-scale invasion as a "special military operation" with several stated goals:
•Protection of Donetsk and Luhansk: President Vladimir Putin framed the operation as protection for residents of the separatist Donetsk and Luhansk regions, and to "save the population from genocide and terrorism".
•Demilitarisation and "Denazification": The stated goals of the operation were demilitarisation and denazification, described as a mission to "demilitarise and denazify" Ukraine. This also included claims of protecting Russian-speaking populations-.
•Response to NATO Expansion: Moscow claimed the invasion was a response to alleged threats posed by NATO expansion. Russia views NATO expansion as a direct security threat, seeing Ukraine's potential NATO membership in particular as an existential red line and the "brightest of all red lines". From Russia's perspective, informal assurances were given in the early 1990s that NATO would not expand "eastward".
•Legal Justification under the UN Charter: Putin offered legal justifications including self-defence under Article 51 of the UN Charter (both individually and collectively with the Donetsk and Luhansk Peoples' Republics) and the protection of Russian nationals. In his speech, President Putin clarified that the basis for the operation is Section 7, Article 51 of the UN Charter, i.e. the right to self-defence.
Some realist analysts argue that Russia's perception of NATO as encroachment upon its sphere of influence fuels a persistent sense of grievance and distrust, and that Russians can point to NATO's eastward expansion and argue that their security concerns were ignored.
The International Law Perspective
The dominant view among international lawyers, the United Nations, and the International Court of Justice (ICJ) is that the invasion violates international law:
•UN Charter: The 1945 UN Charter sets out the conditions under which UN member states may legally resort to war, and prohibits the use of force, except when authorized by the U.N. Security Council or in individual or collective self-defense following an armed attack. Analyses conclude that under no scenario is Russia's armed invasion of Ukraine legal under contemporary international law and norms, and that it can be grasped as illegal precisely because it violated the Charter.
•UN General Assembly Resolutions: On 2 March 2022, United Nations General Assembly Resolution ES‑11/1 deplored Russia's invasion of Ukraine and demanded a full withdrawal of Russian forces and a reversal of its decision to recognise the self-declared People's Republics of Donetsk and Luhansk. The resolution passed with the support of 141 members of the 193-nation body at a rare emergency session. On October 12, the General Assembly adopted Resolution ES-11/4, condemning the attempted annexations.
•International Court of Justice: The ICJ rejected Russia's argument that because it was basing its use of force on self-defence under article 51 of the UN Charter, the Court had no jurisdiction. In March 2022, the Court ordered provisional measures demanding the suspension of Russian military operations, noting that Putin expressly referred to stopping genocide as the purpose of Russia's use of force. The Court also rejected the factual basis for the genocide allegation used to justify the invasion.
Counter-Arguments to Russia's Security Rationale
Critics of Russia's justification argue:
•That the argument that NATO expansion forced Russia's hand collapses because Russia invaded to prevent a membership that its invasion itself made unattainable.
•That the invasion produced the opposite result of its stated aim to stop NATO expansion, triggering a major expansion of the alliance with Finland and Sweden abandoning decades of military non-alignment and joining NATO following the invasion.
Legal scholars who have evaluated claims of individual self-defence, collective self-defence on behalf of Donetsk and Luhansk, humanitarian intervention, and protection of nationals abroad, have found that none of these justifications stands up to scrutiny.
Summary
In terms of international law as interpreted by the UN General Assembly, the ICJ, and most states and scholars, the invasion is considered a violation of the UN Charter and an act of aggression, and therefore not legally justified.
In terms of Russia's own strategic and political narrative, the Kremlin maintains the operation was a necessary defensive measure to protect Russian speakers, counter alleged genocide, and prevent NATO infrastructure on its border.
Because of these competing frameworks, most Western governments, international institutions, and international lawyers view the invasion as unjustified and illegal, while the Russian government and its supporters maintain it was justified on security grounds.