Guilds have arrived. From level 15, found yours at the harbor Hall for 50,000 gold, pick a two- or three-letter tag and call your crew. There are five ranks, with each one's rights set by the leader, a board and a treasury with a scoreboard of who gave the most.
With the treasury full, the leader buys a guild island. On it you raise the Headquarters, the Fortress, ten towers, four nests and the Workshop.
An island worth having needs defending: other guilds can lay siege to it. The attacker arrives through the whirlpool, the defender sails out of the island harbor, each tower holds for a while and the fortress only falls after everything else. Raiders earn points and knock every defense down a level, but take no gold.
Guild cards send part of every kill to the treasury, and diplomacy allows up to three allies and an eight-hour peace flag.