This is a contested geopolitical question — I'll gather the legal context and the competing justifications to give you a balanced answer.
Russia's full-scale invasion of Ukraine launched on 24 February 2022 has been explained and evaluated differently depending on the framework - legal, security-political, and historical - used to assess it.
1. Russia's Stated Justifications
In his 23-24 February 2022 address announcing a "special military operation," President Vladimir Putin gave several stated reasons:
•To "protect people who have been subjected to abuse and genocide" by the Ukrainian government, and to "protect Russia and our people"
•That the Donetsk and Luhansk People's Republics, which Russia had recognized two days before, had requested assistance in their fight against Ukraine
•The stated aims included "the demilitarisation and denazification of Ukraine"
Other justifications presented by the Russian government and media since then include:
•Genocide/humanitarian intervention claim: The false claim that Ukraine was committing genocide against Russian speakers in the Donbas. The narrative was presented as a humanitarian intervention aimed at stopping a genocide of ethnic Russians and Russian speakers in Donbas.
•Security threat from NATO: The eastward expansion of NATO and the possibility of Ukraine joining NATO, with deployment of US/NATO missiles or military in Ukraine which borders Russia. One of Russia’s primary justifications is the eastward expansion of NATO, which Russia sees as a direct threat to its national security and strategic depth.
•Political/historical claims: That the Ukrainian government is Nazi or partially-Nazi, that there was a Western-backed fascist coup in 2014, and that "denazification" was a goal, and that Ukraine's statehood and historical ties justify action to restore historical justice.
•Legal claim of self-defense: Russia has argued that its use of force is lawful under Article 51 of the UN Charter, which preserves rights to defend against "an armed attack" and to engage in "collective self-defense," specifically to defend the Donetsk and Luhansk People's Republics.
2. Assessment Under International Law
The dominant assessment by international legal scholars, international bodies, and most states is that the invasion violates international law:
•The UN Charter sets out conditions under which states may legally resort to war, and the 2022 invasion can be grasped as illegal precisely because it violated the Charter.
•Article 2(4) of the UN Charter requires members to refrain from the "use of force against the territorial integrity or political independence of any state". The only two exceptions are self-defense and authorization by the Security Council.
•Analysts note that under contemporary international law, self-defense is the only justification for use of force against another country, and that "Under no scenario is Russia's armed invasion of Ukraine legal under contemporary international law and norms".
•Legal experts have generally rejected Russia's official legal justifications:
•On self-defense: Experts argued Russia cannot rely on self-defense because Ukraine has not threatened or attacked any other nation, and because Donetsk and Luhansk are not recognized as separate states under international law, collective self-defense does not apply.
•On humanitarian intervention/genocide: Experts have rejected the argument that the invasion is justified to protect Russian-speakers, noting humanitarian justifications are widely perceived as a pretext and are unsubstantiated by any evidence that Ukraine has committed acts amounting to genocide. Scholars described Putin's allegations of genocide and comparison of Ukraine to a Nazi state as baseless.
•On comparisons to Western interventions: Russia has 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.
Other cited violations include breach of the principles of sovereignty and territorial integrity in the UN Charter, and of agreements such as the 1975 Helsinki Final Act and the 1994 Budapest Memorandum.
3. Responses at the United Nations and International Courts
•At the UN Security Council, Russia vetoed a resolution calling for it to cease its attack, while 11 members voted in favor and three abstained.
•At the UN General Assembly, a resolution condemning the invasion was passed with an overwhelming 141-5 vote majority, with 35 nations abstaining. The March 2, 2022 vote was described as the United States and Israel among the 141 countries that voted in favor, with only five countries voting against: Russia, Syria, North Korea, Belarus and Eritrea.
•Two days into the invasion, Ukraine filed a complaint with the International Court of Justice (ICJ) alleging Moscow falsely claimed acts of genocide as justification for the war, in violation of the 1948 Genocide Convention.
•The invasion has also been described as a crime of aggression under international criminal law.
4. How "Justified" Is Assessed
Whether the invasion is considered justified depends on the standard applied:
•Under international law as interpreted by the UN, ICJ, and most legal scholars: No. The consensus view is that none of the Charter exceptions applied - Ukraine did not launch an armed attack against Russia and the Security Council did not authorize force - making it a unilateral and illegal use of force.
•Under Russia's stated security framework: The Russian government presents it as a necessary defensive and humanitarian action to prevent NATO military infrastructure on its border, stop alleged persecution in Donbas, and ensure Ukraine's neutral status.
•In analytical debate: Some analysts distinguish between cause or explanation and legal/moral justification, arguing NATO expansion or security concerns may help explain Moscow's decision-making without making the invasion legal under international law. Critics of that view argue Ukraine is a sovereign state that must be allowed to choose its own alliances and that NATO is used as an excuse for territorial expansion.
In summary, Russia has offered political, historical and security arguments for its actions, while the UN General Assembly, the ICJ proceedings, and the predominant interpretation of the UN Charter reject those arguments as legal justifications for the use of force against Ukraine.