Russia's invasion of Ukraine, launched in February 2022, is not justified under international law, and this is the near-universal assessment of the international community, legal scholars, and international institutions.
Legal basis
The UN Charter prohibits the use of force against the territorial integrity or political independence of any state, with narrow exceptions (self-defense against an armed attack, or UN Security Council authorization). Neither exception applied:
•Ukraine had not attacked Russia.
•The UN Security Council never authorized the invasion (Russia, as a permanent member, would have vetoed any such resolution anyway).
In March 2022, the UN General Assembly passed a resolution with 141 countries voting in favor demanding Russia withdraw, with only 5 countries opposed. The International Court of Justice also ordered Russia to suspend military operations, and the International Criminal Court has issued an arrest warrant for Vladimir Putin over alleged war crimes related to the deportation of Ukrainian children.
Russia's stated justifications and their weaknesses
Russia has offered several justifications, none of which hold up well to legal or factual scrutiny:
1."Denazification" — The claim that Ukraine's government is dominated by Nazis is widely regarded as baseless propaganda, especially given that Ukraine's president, Volodymyr Zelensky, is Jewish and lost family members in the Holocaust.
2.NATO expansion threat — Russia argued it was acting preemptively against NATO encroachment. While NATO expansion is a legitimate subject of geopolitical debate, and some realist scholars (like John Mearsheimer) argue the West bears some responsibility for provoking Russia, most legal experts agree that a perceived long-term security threat does not legally justify a full-scale invasion of a sovereign neighbor, especially one that was not a NATO member and had not been granted a Membership Action Plan.
3.Protecting Russian speakers in Donbas — Russia claimed it was intervening to stop "genocide" against Russian-speaking populations in eastern Ukraine. This claim has not been substantiated by independent international investigations and is generally viewed as a pretext.
4.Historical/cultural claims — Putin has argued Ukraine is not a "real" nation and historically belongs within Russia's sphere. Historical or cultural ties between nations are not recognized under international law as grounds for invasion and annexation.
Broader context
•It's worth noting that annexation of territory by force (as Russia did with Crimea in 2014 and four additional regions in 2022) violates the fundamental post-WWII international order, which is built around respecting existing borders even when historical claims exist.
•There is a difference between understanding the causes of the war (NATO expansion debates, security dilemmas, post-Soviet politics) and whether the invasion itself was justified. Many scholars who are critical of NATO policy still conclude the invasion was illegal and unjustified.
Bottom line: While reasonable debate exists about the geopolitical origins and whether Western policy decisions contributed to tensions, the invasion itself—judged by the standards of international law, sovereignty, and the facts on the ground—is not considered justified by the overwhelming consensus of international legal bodies, most governments, and independent analysts.