Well, both actually. At the point you're controlling the water you have the luxury of naming who and when you fight. Coasts are generally long enough that you've got several options and nobody is realistically going to be attacking you at this point. In the vast majority of cases you can just sit there until you can surprise attack someone who is already in a fight with no real need to defend your long border. Even once you've got a big bite of land you've got serious negotiating leverage as nobody really wants to fight with you when 2/3rds of your territories are underwater, and you can also potentially attack on another coast which doesn't touch your other land holdings. Artifacts was (is?
) hideous in how quickly everyone piled on anyone who got at all ahead but in my experience this is not how things usually play out. It seems to me much more common for you to make a good war ally in your first or second war and have solid backup going forward.