No, you don't have to sell any harbors if you disconnect the roads around your capital. If you kept roads around your capital, you could pillage at your borders instead, so long as you don't have any trade routes via a harbor. I would advise using your capital. I have the AIs set at "least aggressive". On top of this, if they don't feel at least "polite" to me, I'll generally try and gift them 100 gold (which I promptly buy back in trading) to try and improve their attitude towards me. The gpt going to them, also probably helps to keep them at peace with you. Wait... that's just to keep a sneak attack. You also have to make sure NOT to export any luxuries/resources to the AI. This wouldn't necessarily cause war, but would cause a reputation hit, and consequently make a sneak attack more likely, I think.
When I want a war, I basically make sure I can "purchase" some resource/luxury from the target AI, and that I can also re-negotiate a peace treaty. Then I open up the diplomacy screen and click on "Active" at the bottom of the screen. I re-negotiate the peace treaty with gpt going to the AI for a luxury/resource and anything else like workers (if any available) and lump sums from the AI. Now, I also do NOT export any luxuries or resources to the AI. They import luxuries or resources to me tied to the peace treaty for gpt. Then, I pillage the trade route to my capital. This results in the AI declaring on me (I don't think I did this in the Iroquois game all that much, and only figured it out in my China large game or my abandoned huge game with China, which I've mentioned in my HoF write-up thread). I try to do this on my
first pillage with a resource if say I have a disconnect/reconnect for horses-knights upgrade thing going on.
Now, what if the target AI has no extra resources/luxuries available? I then try to figure out which resource luxury I have the least number of/have in some corrupt area far away from my productive core. I park one unit, as weak as I have basically (in this game, I've used javelin throwers and rifles mostly for this) one square adjacent (on a road, of course) to any of those cities. Next, I open up the diplomacy screen. I then gift those cities with the resource/luxuries to the target AI. Then, I open up the diplomacy again, and I double check to see that the target AI now has an extra resource/luxury available for sale. If not, I'd check the F2 screen to see where I still have an extra resource/luxury.
Then, if later in the game especially, I'd make sure I can pay gpt for that resource/luxury before doing any actual deals (use tax collectors/adjust tax slider temporarily as needed). Once I feel sure of this, I'll re-negotiate the peace treaty with the AI, again, with a resource/luxury coming from them with only gpt going to the target AI (you could theoretically use techs/lump sums you have also, but why would you give an AI techs/lump sums before going to war?). Then, I'll cut the trade route. Since the exporter of a luxury/resource comes as responsible for continuing the trade deal, and the resource/luxury deal comes as tied to the peace treaty, the AI declares on me.
Then I re-connect the road, and acquire gpt with my lump sums of gold if any available with any AIs with a luxury/resource available. With least aggressive AI the rate goes 18 gold for 1 gpt. I'll then sign military alliances (on turns when starting a war, if I want a military alliance), as many as possible tied to resource/luxury deals, and re-acquire all those lump sums by sending the AI gpt for resource/luxuries, along with techs or workers or maps if available. Then I'll cancel all of those deals by cutting the trade route... but the hard goods (workers/gold/maps/techs) stay with me. The deal where I leeched gpt from the AI stays in tact, since I sent them a lump sum for gpt (no resources/luxuries involved). I then reacquired the lump sum giving me both.
Then I cut the trade route once more. I re-connect and pay gpt for the luxuries. Note that I
first disconnect the trade route before doing any lump sum for gpt deals, because I do NOT want to put any more money into the world economy than already exists there (which the HoF rulebook says does not work for Conquests, but even so, I'm not so sure about this... and I might not want to hurt every AIs economy as much as I could, which might result if I did this, because I want the AIs to do research for me).
I
just take whatever already exists in the world's economy/workers/maps/techs and put them into my hands. Note that I haven't given the AI anything really, as all deals get cancelled immediately (except for the final one involving luxuries/resources for gpt only). I also haven't given the AI more gpt than I can afford, since all of that gpt I could have payed had I wanted to for some reason.
What I've described (as indicated by others also) comes as legal under HoF rules according to this clause
I didn't come up with this. I first learned of the basic idea, and didn't understand it actually when reading a Sid succession game, where Ignas suggested something like this (Microbe seems to have noticed the basic thing long before this). Lord Emsworth explained many of the details of what you can do with this
here. The only thing possibly new with me (I'm not so sure Lord Emsworth didn't hint this at me either) comes as to use the capital instead of your borderlands. After a few games of playing both ways, I definitely feel the capital easier to use on a pangea map, and it basically comes as the only option on an archipelago map (I haven't tried selling/buying harbors on and off, and it seems even more expensive).
That all said, it *can* fail (though I doubt often), or at least disappoint you. When starting a war, as I learned in my abandoned pangea Huge game with China you have to make sure you can re-negotiate the peace treaty (which you can ensure by NOT getting into any wars with the target AI before attacking them). Also, I'll mention that in this game I wanted to attack the Hittites first. They had extra incense and I think gems for a while. I didn't trade for them, as I had planned to attack them once I had built up my military, so I wanted to make sure I could get them from someone else. The turn I wanted to start a war with them (though not the previous turn), they had no luxuries or resources to trade for, as I recall. Fortunately, I investigated one of their border cities, saw they had 7 luxuries going for them, and found some way to get them the 8th which I had, and started the war. So, I managed.