The treaty is large, but the idea is obvious.
Before that, what invaders did was encircle cities and starve them out.
The 1906 Hague Conventions, which turned into the Geneva Conventions, made that illegal.
Do you disagree?
So you disagree that starving out countries into surrender, like we did to Germany in WWI, is immoral and unethical?
Submarine warfare originally was illegal unless it surfaced and forced ships to surrender.
Who and why do you think that got ignored?
Just consider the US constitution.
If we have freedom of political expression, that has to include being free to conduct business with the political ideas we believe in, regardless of the country they are practiced in.
So economic sanctions against Russia, Iran, etc. is dictating our political and economic associations, and is totally and completely illegal under US law.
But I did run into this:
{...
Rule 53. The use of starvation of the civilian population as a method of warfare is prohibited.
Summary
State practice establishes this rule as a norm of customary international law applicable in both international and non-international armed conflicts.
International armed conflicts
While in 1863 the Lieber Code still stated that “it is lawful to starve the hostile belligerent, armed or unarmed, so that it leads to the speedier subjection of the enemy”,[1] by 1919 the Report of the Commission on Responsibility set up after the First World War listed “deliberate starvation of civilians” as a violation of the laws and customs of war subject to criminal prosecution.[2] The prohibition of starvation as a method of warfare is codified in Article 54(1) of Additional Protocol I.[3] This provision was generally considered new at the time of the adoption of Additional Protocol I but since then has hardened into a rule of customary international law. Under the Statute of the International Criminal Court, “intentionally using starvation of civilians as a method of warfare” is a war crime in international armed conflicts.[4]
The prohibition of starvation is set forth in numerous military manuals.[5] Starvation of civilians as a method of warfare is an offence under the legislation of many States.[6] This rule is also supported by official statements and other practice.[7] This practice includes that of States not, or not at the time, party to Additional Protocol I.[8] Contrary practice has been generally condemned or has been denied by the accused party.[9]
...}
afripol.org
And economic sanctions essentially are starvation warfare, only to a slightly lesser degree.