How exactly do you enforce such a law? If the victor refuses to follow the law, invade their country, set up a new puppet government, and put them on trial?
With your approach there's always the risk that your sanctions are worse for the population than the consequences of the mines, particularly because economic damage is compounding.
You can sanction the individual oligarchs versus the country wholecloth perhaps. Ban the oligarchs from travel, deny their private jets over allied airspace, deny their boats a right to port, offer a bounty for their boats in international waters. Seize their foreign assets. Ban them from participating in your markets. Make participating in the fun of the global high society annoying to impossible, and force them to be on house arrest in their own country. Do the same for their extended families living abroad and their close friends. Kick their children out of foreign private schools. Jail the kids. Do the same for the oligarchs in any country who doesn't want to align with the UN on this issue.
There's plenty of things that could be done beyond what has been done typically.
They've done all that stuff and more (including seizing their boats) for Russian oligarchs and it hasn't changed anything. In fact, a bunch of those oligarchs have committed suicide as a result, frequently by shooting themselves in the backs of their heads and then jumping out of windwos.
In theory, it’s irrational to give into threats in iterated games, or in one-shot games where your opponent can look at your code. (“We don’t negotiate with terrorists.”) So threatening sanctions shouldn’t work.
But in practice, when everyone knows you have a bazooka, you might not ever have to fire it.
