It basically requires two governments consenting to grow the trade route to a moderate or major OR for a non-trade center city to increase it's LPs enough. Look at the Eastern Mediterranean-Indian cultures for examples.
Also, since I'm
just now realizing that we're going to get to the point where there are thousands upon thousands of LPs circulating, I'm reforming the combat rules only slightly so that I don't do an individual roll for each combat round (like I did in RIOT). This means an extra twelve hours won't be slapped onto how long it takes to update.
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Basically, say that an attacker is using 10 LPs to attack a territory defended with 5 LPs. Defenders get a 20% defensive bonus (meaning the 5 LPs becomes 6 for combat purposes). I add up the 6 and 10 (equaling 16) and do a 1-16 RNG roll. 1-10, Attacker wins. 11-16, Defender Wins.
So, cities give a 20% defensive bonus, defending 20%, each epoch above your opponent 20%, amphibious landing is a 20% penalty, etc.
There are no defensive bonuses at seat though. Just technology bonuses.
When I go and calculate how many LPs are lost (if any), it'll simply be how far away the RNG number is from the opponent's number zone. So, say that I roll a 15 (Defender Wins), the Attacker (if he was using Countryside LPs) loses 5 LPs.
In other words, only two RNG rolls for a single battle.
As opposed to the +500 rolls I did for a large mid-game battle RIOT.