Is Russia's invasion of Ukraine justified?

This is a question about a factual/legal matter with a clear international consensus, though it also touches on issues where people hold different political views. Let me give you the relevant facts.

International legal consensus:

Russia's full-scale invasion of Ukraine, launched in February 2022, has been widely assessed as a violation of international law by the vast majority of the world's states and legal scholars. The United Nations General Assembly passed resolutions condemning the invasion by overwhelming margins (141 countries in favor of the initial condemnation resolution, with only a handful of countries—including Belarus, North Korea, Syria, and Eritrea—joining Russia in opposition).

The core legal issue is straightforward under the UN Charter: Article 2(4) prohibits the use of force against the territorial integrity of another state, with narrow exceptions (self-defense against an armed attack, or UN Security Council authorization). Ukraine had not attacked Russia, and there was no Security Council authorization for Russia's action. The International Court of Justice and International Criminal Court have both taken up cases related to the invasion, with the ICC issuing an arrest warrant for Vladimir Putin in 2023 over alleged war crimes.

Russia's justifications and why they're widely rejected:

Russia has offered several justifications—claiming it was preventing NATO expansion, protecting Russian-speakers in Donbas from alleged genocide, and "denazifying" Ukraine. These claims have been extensively scrutinized and largely rejected by independent investigators, historians, and legal bodies as lacking credible evidentiary support or as not meeting the legal threshold for justified use of force under international law (e.g., "preventive self-defense" against a potential future threat is not recognized as lawful).

Where reasonable disagreement exists:

There is legitimate debate about related questions—NATO's post-Cold War expansion policy, Western strategic missteps, the wisdom of specific Western responses, or the complex history of the Donbas conflict since 2014. Some scholars (realist IR theorists like John Mearsheimer, for instance) argue Western policy created conditions Russia found threatening. This is different from arguing the invasion itself was legally or morally justified—most who make this argument still don't claim the invasion was lawful, only that it was foreseeable or provoked.

Bottom line: Under international law and by near-global consensus, the invasion is considered a war of aggression and not justified. If you're interested in the specific historical, geopolitical, or legal arguments on any side, I'm happy to go deeper into any of them.