What do you mean by "appropriation of the oceans"?

Here’s the sentence that I couldn’t understand that I read in ETS site


From the beginning, it was easy to argue against the idea that seas were free from being claimed by any particular nation.
This was because there also existed the idea that the waters in particular areas could be claimed by countries and nations in order to make profits (from fishing rights, etc.) and as a means of national security (so that no one else could enter those waters without permission).

appropriation of the oceans: the taking of the oceans (by a country) for their own use.