Is Russia's invasion of Ukraine justified?

This question involves competing legal, moral, and political claims, so let me lay out the widely-documented facts and perspectives rather than render a personal verdict.

The dominant international legal and factual consensus

The overwhelming majority of the international community, most legal scholars, and the United Nations General Assembly have characterized Russia's actions as a violation of international law—specifically of the UN Charter's prohibition on the use of force against another state's territorial integrity and political independence, and of Ukraine's sovereignty as recognized in agreements like the 1994 Budapest Memorandum (where Russia pledged to respect Ukraine's borders in exchange for it giving up Soviet-era nuclear weapons).

The UN General Assembly passed resolutions (with over 140 countries in favor) condemning the invasion and calling for Russian withdrawal. The International Court of Justice and International Criminal Court have also taken up related legal actions, including an ICC arrest warrant for Vladimir Putin over alleged war crimes.

Russia's stated justifications

Russia has offered several rationales, including:

Most independent historians, legal experts, and Western governments have rejected these as pretexts, arguing they don't meet the legal threshold for self-defense under international law and that evidence for claims like genocide against Russian speakers has not been substantiated by independent investigators.

Where reasonable debate exists

Some geopolitical analysts (a minority view, notably associated with the "realist" school like John Mearsheimer) argue NATO expansion provoked a security dilemma that made conflict more likely—this is a debate about causes, not necessarily a justification. It's important to distinguish "explaining why something happened" from "justifying it as legal or moral."

Bottom line

Under the framework of international law as currently constituted and interpreted by most global bodies, Russia's invasion is widely considered a violation of Ukrainian sovereignty and the UN Charter. Whether you find Russia's security or ethnic-protection arguments morally persuasive is a separate, more subjective question—but they have not been accepted as legally justifying grounds by the international community, courts, or most scholars of international law.

If you want, I can go deeper into any specific angle—NATO expansion history, the Minsk agreements, legal arguments under Article 51 self-defense claims, etc.