Blockades – Aside from normal port blockades, you can also blockade enemy ships from dropping off enemy troops along the shore. The red areas indicate blockading range of your ships. A neutral fleet can also blockade you if you hit them along the path unaware. Thus, it is ideal to not hug the coast too tightly when traveling.
(normal port blockades) Seaports can be blockaded from land or sea. Place the land unit inside the port or move the ship to attack the harbor.

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