I've been giving this some thought. This is my first attempt to put my thoughts into game form....
My proposal for changes to the mechanics of CIV5 FOREIGN TRADE: it would provide a fairly substantial benefit to maintaining trade routes with foreign civs. There would be 3 ways to establish a foreign trade route with other civs: 1) via land routes, 2) overseas with civs on same continent, and 3) overseas with civs on other continents.
Global Rules:
1) Foreign trade routes require an active trade agreement that is NOT a money-for-money exchange.
2) For every foreign trade route established, the player receives a base +1 gold into treasury. Additional gold may also be provided (see bonuses below).
3) Note: it is possible for the player to NOT have a foreign trade route established with another civ, and yet still be trading strategic or luxury goods, or engage in any other sort of trade. Failure to establish a foreign trade route simply means that the player does NOT obtain the bonuses (see below).
Foreign Trade divided into three types: overland continental, overseas continental, overseas international.
1) Establishing a Foreign Trade Route:a foreign trade route is established in one of three ways:
--A) Overland Continental: trade existing from land routes between civs located on the same continent
---->requires:
--------(1) open border agreement &
--------(2) road built connecting at least 1 player controlled city to at least 1 city belonging to foreign civ.
--------------Note: Road may pass through other civs IF open borders agreement exists w/ third-party civ
--B) Continental overseas: coastal trade existing between civs located on same continent.
---->available with Sailing
---->requires:
-------(1) open borders agreement with other other civ, &
-------(2) city must be connected to the capital by a road &
-------(2) city must have harbor built.
--C) International overseas: overseas trade existing between civs located on different continents.
---->available with: Navigation
----requires:
------(1) must have open borders agreement with other civ &
------(2 )city must be connected to capital by road &
------(3) city must have Harbor built &
------(4) city must have Market built.
2) Foreign trade route bonuses:
----> additional +1 gold for all foreign trade routes during Classical era. Bonus ends w/ entering Medieval era.
----> +1 gold with discovery of Economics (restructuring of economies around colonization)
----> +1 gold with discovery of Railroad per overland continental.
----> +1 culture with discovery of Flight for every foreign trade route.
----> +1 gold per international overseas trade route with Computers.
3) It is possible for all foreign trade to be blockaded -- by enemy warships blockading coastal cities combined with being surrounded by closed borders.
-->Scenarios:
----(A) It is possible for enemy to blockade intercontinental overseas routes, while continental overseas routes remain open.
----(B) It is possible for only overland routes to be blockaded
--------> Note: if continental overseas routes are blockaded, then intercontinental overseas routes must necessarily be blockaded too.
-------->Only bonuses to foreign trade routes are lost. Trades would remain active.
I think these changes (or something along these lines) would create real incentives to engage in foreign trade, but such would require managing the peace, building early infrastructure, but also exercising skill in keeping the routes open.
I also think these changes could be implemented nicely along side changes in the game's coding that makes barbarian pirates more of a factor requiring more battling to keep trading lanes open. I'm thinking about how big of a role piracy has played throughout history -- I'd like to see it given more prominence in CIV.
Anyways.....feedback?