Article 2(4), asked in plain words

A Member uses force to take back a disputed province. The question goes in as a sentence; what comes back is a rule of the Charter, its premises, and an answer that moves when one fact changes.

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Aurelia, a Member of the United Nations, used force against Borealia to take back a province both claim. Borealia had not attacked Aurelia. Does that breach the Charter?

Let me find where the Charter speaks about this, in your words rather than mine.

Article 2(4). Before I answer, I want the rule itself — what it needs and what can defeat it.

Two premises: force used by one State against another, and the first State being a Member. One way out: an armed attack by the other State, which brings in Article 51. Your facts give me both premises and no attack. Let me ask with exactly those.

Established: on these facts the use of force breaches Article 2(4). The engine also names what would defeat the answer — an armed attack by Borealia on Aurelia. Let me show that the answer really does turn on that fact.

Refuted: with an armed attack by Borealia on file, Article 51 applies and the breach falls away. The engine then names what would defeat that in turn — the Security Council having taken measures. So on your facts the answer is a breach of Article 2(4). The whole answer turns on one fact, whether Borealia attacked first, and that fact is yours to prove, not mine to assume.