You're mixing up personal jurisdiction with legislative jurisdiction. There is a body of customary international law that concerns the appropriate scope for ext

You're mixing up personal jurisdiction with legislative jurisdiction. There is a body of customary international law that concerns the appropriate scope for extraterritorial legislative jurisdiction. This is separate from personal jurisdiction, which is in some ways easier to establish. In the US, for example, you can get personal jurisdiction over any natural person, and sue them for any way they wronged you anywhere in the world, merely by serving them with process while they are physically present in the US. But if you sue someone in Alabama for something they did in France, the Alabama court is going to apply French law in most cases. (in most countries, there is also something like the common law doctrine of forum non conveniens that allows courts to dismiss cases that are better heard by a court elsewhere) And it's simply not the case that foreign judgments are generally unenforceable. See the discussion here https://en.wikipedia.org/wiki/Enforcement_of_foreign_judgments https://en.wikipedia.org/wiki/Enforcement_of_foreign_judgmen... . No treaty is necessary, though it certainly helps the person seeking enforcement if there is one.