[Sebb767]

The big problem, as a sister comment pointed out, is that, for various reasons, a lot of people live close to the coast line. And a lot of people having to move was historically never really a good for peace, plus we loose a lot of agriculturally valuable land in the process.

[_0w8t]

Transportation by water is like 50 times cheaper than by land and it has been like that for at least the last 2000 years. So most people live either along the coast or along rivers.