There should be certain territories for which it would be necessary to control a "blockading" territory in order to attack/fortify. For example, if territory A and B were regular territories and territory C was a blockading territory, it would be necessary for one to control territory C in order to attack/foritfy from territory A to territory B.
Why blockading territories should be implemented
#1To accurately simulate naval warfare and the idea that an army can't cross a body of water dominated by enemy ships.
#2 De-facto truces. If Player 1 controls territory A and has 500 armies on it while Player 2 leaves only one army on territory B while he has 500 armies on territory C, there would be a De-facto truce. It would be more difficult for Player 1 and 2 to attack each other because they would need to fortify their armies or spend several turns building up in order to attack each other. De-facto truces would allow players to more easily focus on attacking a specific target instead of trying to play a build game.
I am thinking about making a Pacific ocean map based on blockading territorities if they are implemented
