Shadowbane did it right.
Make all owned islands fairly crap when it comes to resources, make lawless rich in resources, and have declarations of war for when you want to raid. Your own island will be crap but bases/green anchored ships unraidable (not players immune to damage like it is now), and you'll need to visit lawless to get good loot (lawless don't need to be right outside freeport either but it's not terrible). This will spur lots of movement and ship combat and transport, and will make those islands you want to take actual fights.
Most of the land fighting will be done on the brutal ruleset of lawless as people try to secure good loot spawns for themselves, and when the pressure builds they will go to war with the group pestering their spot.
Lower the cost on war declaration too, so it's frequent if necessary (after the 'cooldown period'), but also costly to the attacker.
Beyond all that, the game has 1000 bugs and annoyances that should be fixed too.
At least the game is in a great state and feels so much fun playing it again.