The killing civilians bit or the destruction of personal property, like homes, bit.
Or, to be more specific, the First Protocol, dated 1977:
Article 51 - Protection of the Civilian Population (
Link)
"
2. The civilian population as such, as well as individual civilians, shall not be the object of attack. Acts or threats of violence the primary purpose of which is to spread terror among the civilian population are prohibited."
Article 52 - General protection of civilian objects (
Link)
"
1. Civilian objects shall not be the object of attack or of reprisals. Civilian objects are all objects which are not military objectives as defined in paragraph 2.
2. Attacks shall be limited strictly to military objectives. In so far as objects are concerned, military objectives are limited to those objects which by their nature, location, purpose or use make an effective contribution to military action and whose total or partial destruction, capture or neutralization, in the circumstances ruling at the time, offers a definite military advantage."
Oh, no, hang on. Russia can't contravene these artciles because it withdrew from the protocol in 2019. The only country to do so.
https://ihl-databases.icrc.org/appl...Pages_NORMStatesParties&xp_treatySelected=470
https://thehill.com/opinion/interna...convention-protocol-sets-dangerous-precedent/
Anyone would think it was getting itself ready for a bit of scorched earth policy.