Blockades

[EatYerGreens]

There is a sort of logic to the 'land bridges'. Bear with me while I explain.

I think the game manual itself explains how the ships which actually carry trade goods overseas are, in effect, invisible in the game. The ships you build for yourself in the game are actually military only. They enable you to control a sea region and blockade passage of an enemy faction's (again invisible) trade vessels, whilst meantime defending the safety of your own traders.

I see the land bridges as representative of your armies 'renting' the use of trade vessels to make a short sea crossing.

The significance of the 'bridges' is that they are in places where the opposite coast can be sighted from land, so they are long established travel routes. Hardly a navigational challenge, when never out of sight of land, eh?

Longer distances, more challenging navigational requirements and beach landing invasions require a proper navy.

EDIT: Extending this logic would seem to demand a land bridge between the Mull of Kintyre, in Scotland and the NE tip of Ireland as it's possible to sight one coast from the other, with decent weather. However, some may say that it makes things a little too easy for the English to unite the Isles and spam Gallowglasses for the rest of the campaign...