Is Russia's invasion of Ukraine justified?

This is a question with both a factual/legal dimension and a political one, so let me separate those.

On international law:
The invasion is widely considered illegal under international law. The UN Charter prohibits the use of force against the territorial integrity or political independence of another state (Article 2(4)), with narrow exceptions for self-defense or UN Security Council authorization. Neither applied to Russia's 2022 invasion—Ukraine had not attacked Russia, and the UN Security Council did not authorize the action (Russia, as a permanent member, would have vetoed any such resolution anyway). The UN General Assembly passed a resolution shortly after the invasion with overwhelming majority condemning the Russian invasion as a violation of Ukraine's sovereignty and territorial integrity. The International Court of Justice and International Criminal Court have also taken actions reflecting this view, including an ICC arrest warrant for Vladimir Putin related to alleged war crimes.

Russia's stated justifications and their reception:
Russia has offered several justifications: protecting Russian-speaking populations in eastern Ukraine, preventing NATO expansion, "denazification" of Ukraine, and historical/cultural claims that Ukraine is not a legitimate separate nation. These arguments have been rejected by the overwhelming majority of the international community, including most UN member states, as pretexts that don't meet the legal threshold for the use of force. Independent assessments have found no credible evidence of genocide against Russian speakers prior to the invasion, and NATO's eastward expansion, while a real geopolitical concern for Russia, is not a recognized legal justification for invading a sovereign neighbor.

Where there's more debate:
Some realist foreign policy scholars (e.g., John Mearsheimer) argue that Western/NATO policy toward Ukraine provoked Russia and that the war was foreseeable or even partly caused by Western actions—this is a debate about causation and wisdom of Western policy, not a legal justification for invasion. This view remains a minority position among international law experts and Western governments, though it has some adherents in academic and policy circles.

Bottom line:
Under the prevailing international legal framework and the view of most of the world's governments and legal bodies, the invasion is not justified. There are legitimate debates about the geopolitical context, NATO expansion, and Western policy choices leading up to 2022, but these are generally treated as separate from the question of whether the invasion itself was lawful or justified—on that narrower legal question, the international consensus is clear.

If you want, I can go deeper into any one angle—international law specifics, Russia's stated rationale, the NATO-expansion debate, or how different countries/blocs (e.g., Global South) have voted or responded.