Wow, these are all great ideas! For the first time I'm not really sure which way to go with this game... sooooo many options open to us.
Those Summarians are fiesty little guys, and truthfully I'm not sure if we're strong enough to take them out in one push now. Besides, if we wait just a little bit longer, Summaria will be done making Ekidu, and making something stronger. Which means no GA if we attack MDI with knights instead of Ekidu with Swords.
Mongolia on the other hand is going to get the Keshik very soon. Takes the place of their knights, and they're more likely to attack us the Summaria, even if we are the same cultural group. They may have a few Keshik's built by the time we invade, but if we take out Summaria first, they will have alot more, and Keshiks are rough all the way up to Industrial Ages. If we take Ta Tu and Alamarikh, we will make a good choke point, where we can seal them off, and ensure we can take them at our pleasure.
Summaria also has a much wider front then Mongolia does, and they're more into building then warmongering, which means they may have alot of Ekidu, but not going to have much else in 50 turns.
Now if we do go over the Mongols, we'll have to consider if we're going to take those 3 cities, and call it quits, or destroy them. If we are going to destroy them, it's going to take a little while. Instead of signing a RoP with Byz, maybe we should sign an MA against Mongolia with them. It will weaken both of them to be warring, Byz will only get a few of their smaller corrupt cities near their contient, while we can take their mainland. Once we did that, a palace move to Boston would be crucial. The FP is in Wonson, which is close to both the Old and New Capitals. Another plus for going after Mongolia is city size. Most of their "cities" are really villiages which means no defensive bonus, and 2!! Ivory! We'd be rich! We're probably the only other people with Ivory in the world.
Rush some barracks to help starve down American cities, upgrade our Swordman, and take on Mongolia within 10-15 turns, taking Ta-tu, Almarikh, and Darhan for sure, and maybe taking out Karakorum to destroy their culture. Karakorum would be an even better choke point then Ta-tu now that I look at it more. Raze, and rebuild it, and we won't have to worry about flipping of the other cities.
The more I think about it, the more and more I like the idea of taking out Mongolia with troops from the core, while we build up the new cities. If we take the fight only to Karakorum, they will be crippled which means we can sue for peace for 20 turns, turn to Summaria and take them out after they upgrade their Ekidu, then if we still have gas left return to Mongolia to finish off their last few cities.
We still need to figure out if we should sign Byz to an MA or or an RoP to take out Mongolia, or both.