This is a question I want to answer carefully and honestly, giving you substantive information rather than a hedge.
The mainstream international legal and factual assessment is that the invasion is not justified. Key points:
•International law: The UN Charter prohibits the use of force against the territorial integrity of another state except in self-defense or with Security Council authorization. Ukraine did not attack Russia. In March 2022, the UN General Assembly voted overwhelmingly (141-5) to condemn the invasion and demand Russian withdrawal.
•Sovereignty and prior agreements: Ukraine's borders (including Crimea) were recognized by Russia itself in multiple treaties, including the 1994 Budapest Memorandum, in which Russia, the US, and UK pledged to respect Ukraine's sovereignty and borders in exchange for Ukraine giving up Soviet nuclear weapons.
•Russia's stated justifications — that it was preventing "genocide" in Donbas, that Ukraine posed an imminent NATO military threat, or that Ukraine isn't a "real" nation — are widely rejected by independent historians, legal scholars, and most governments as pretexts. No credible evidence supports genocide claims against ethnic Russians in Ukraine prior to 2022, and NATO membership was not imminent.
•War crimes evidence: Independent investigations (UN, ICC, human rights organizations) have documented attacks on civilian infrastructure, mass graves, deportation of children, and other alleged war crimes attributable to Russian forces, which further undermines the legal/moral case.
•The ICC has issued an arrest warrant for Vladimir Putin over alleged war crimes related to the unlawful deportation of Ukrainian children.
Where there's more legitimate debate: Some analysts (realist scholars like John Mearsheimer, for instance) argue NATO expansion provoked Russia and that the West bears some responsibility for the geopolitical tensions leading up to the war. That's a different claim, though — it's an argument about contributing causes, not a legal or moral justification for launching a full-scale invasion of a sovereign neighbor.
If you want, I can search for more current details — like the latest ICC proceedings, territorial status, or specific incidents — happy to dig into any angle.