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.
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.