I think we take for granted that they are clearly defined now because nation-states worked very hard to define, create, and enforce that concept. As I understand it, for most of human history there was no real notion of a well-bounded state and even today sovereignty is hotly debated in some areas.
So, it's not that enforcing land borders is intrinsically easy. It's that it appears easy because nations adopted it as their responsibility and do the work. Look at how much political energy was expended around Trump's wall between the US and Mexico to get a sense of how complex and effortful land borders are.
I don't see any reason that Internet sovereignty couldn't be equally well-defined and defended... except countries simply aren't doing it.
The difference is that the geographical boundaries of nations are (to a large extent) found, not made. So the lines of defense run along natural ones. If you're talking about building one on the internet you're talking effectively about creating the equivalent of the Chinese firewall.
The inter-net as the name suggests is a network, not a perimeter and runs across boundaries. If you want Trump's border wall on the internet you're talking about handing the government sole access and control to all information going in and out.
That's way beyond cyber defense of private business. And looking at some countries engaging in this right now you better be careful what you ask for.
Boundaries are established, they are not "found". Algeria, Angola and Namibia. Check the borders of those 3 countries, there is nothing natural about those borders.
Countries try to enforce their borders. And they normally regulate traffic through a custom, the rest is deemed unlawful.
More on the point: the current internet is a mess. Hopefully it collapses and a new network is built, with security in mind this time.
I think we take for granted that they are clearly defined now because nation-states worked very hard to define, create, and enforce that concept. As I understand it, for most of human history there was no real notion of a well-bounded state and even today sovereignty is hotly debated in some areas.
So, it's not that enforcing land borders is intrinsically easy. It's that it appears easy because nations adopted it as their responsibility and do the work. Look at how much political energy was expended around Trump's wall between the US and Mexico to get a sense of how complex and effortful land borders are.
I don't see any reason that Internet sovereignty couldn't be equally well-defined and defended... except countries simply aren't doing it.