We need technological solutions for this problem, not new international laws or, holding nations accountable and so on. Nations, including the US, will always try to exploit weaknesses in computer infrastructure. We need a fundamental rethink of the technical underpinnings of the internet. Such as air-gapped systems, or something that is physically isolated from foreign access.

So for example, in order to access a critical government system you need a dedicated, physical wire running to your computer. This may mean no access from home and that's fine.