Is Russia's invasion of Ukraine justified?

Your question touches on international law and contested history — I'll gather the competing justifications and legal findings to give you a balanced overview.

Russia's full-scale invasion of Ukraine on 24 February 2022 is widely assessed under international law as illegal, though Russia has offered its own legal and political justifications for it.

What Russia claims as justification

On 23-24 February 2022, President Vladimir Putin announced a "special military operation" in Ukraine. He claimed that:

In public speeches and state media, the operation was also framed as:

Other official claims have included preventing Ukraine from acquiring nuclear weapons and protecting Russian speakers in the Donbas.

Scholars described Putin's allegations of genocide and comparison of Ukraine to a Nazi state as baseless.

How international law assesses those claims

Since the beginning, the Russian invasion of Ukraine has been described as violating international law (including the Charter of the United Nations). The invasion has also been called a crime of aggression under international criminal law.

The legal framework is the 1945 UN Charter, which sets out the conditions under which UN member states may legally resort to war or the use of armed force. The 2022 Russian invasion can be grasped as illegal precisely because it violated the Charter.

Key Charter provisions:

Many experts on international law have opined that the invasion violated Article 2(4)'s prohibition on the "use of force" and have rejected Russia's official legal justifications.

Analysis of the specific justifications:

1. Self-defense / collective self-defense under Article 51
Russia has argued its use of force is lawful under Article 51 of the UN Charter, which preserves rights to self-defense and collective self-defense, to defend the Donetsk and Luhansk People's Republics.
Experts such as John B. Bellinger III, Gabriella Blum, Naz Modirzadeh, and Anthony Dworkin have criticized this argument. They argue Russia cannot rely on self-defense because Ukraine has not threatened or attacked any other nation, and even if Ukraine had been planning an attack against Donetsk or Luhansk, Russia could not invoke collective self-defense because these regions are not recognized as separate states under international law.

General assessment: Self-defense is the only justification for use of force against another country, according to international law, and under no scenario is Russia’s armed invasion of Ukraine legal under contemporary international law and norms.

There is simply no plausible legal justification for the invasion, and Putin's attempt at creating one through recognizing the 'people's republics' and then claiming collective self-defence and the need to protect them from Ukrainian 'genocide' is obviously baseless. Russia's invasion violates the UN Charter and cannot be justified under international law as an act of self-defense or humanitarian intervention.

2. Genocide / humanitarian intervention to protect Russian speakers
Experts have rejected Russia's argument that its invasion is justified on humanitarian grounds to protect Russian-speakers in the Donbas. Even if humanitarian intervention were accepted in international law — which is heavily disputed — it would require an actual threat and a minimum of force, conditions not met here.

In any event, Russia's humanitarian justifications are widely perceived as a pretext, and are unsubstantiated by any evidence that Ukraine has committed acts against Russians in Donetsk and Luhansk that could amount to genocide.

The International Court of Justice (ICJ) in The Hague ordered Russia to immediately suspend military operations launched on February 24, 2022, stating there was no evidence to support Russia's claim that Ukraine was committing genocide in the eastern regions. At the present stage, the Court is not in possession of evidence substantiating the allegation of the Russian Federation that genocide has been committed on Ukrainian territory. The ICJ also ruled there was no evidence to support Russian claims of genocide in Luhansk and Donetsk.

3. Comparisons to Western interventions
Russia has also tried to justify its invasion by comparing it to interventions by the US and allies in Kosovo, Iraq, Libya, and Syria. These comparisons have been dismissed as irrelevant because one illegal act does not make a different act legal. Professors Blum and Modirzadeh remarked that "even if [they were] true, one illegal use of force does not justify another".

4. Violation of other agreements
The invasion also was said to violate international agreements Russia is party to, including the 1994 Budapest Memorandum, in which Russia, the United States, and the United Kingdom agreed "to respect the independence and sovereignty and the existing borders of Ukraine", as well as the 1975 Helsinki Final Act and Minsk agreements.

Response of the United Nations and international courts

Summary

Whether a use of force is considered "justified" therefore depends on the framework applied — legal assessment under the UN Charter versus Russia's stated political-security rationale. The overwhelming international legal consensus is that the Russian justifications do not provide a lawful basis for the invasion under contemporary international law.