Yeah, Karakorum is an absolutely ridiculous city. Lots of production, obviously (that's how it got however many wonders it has) plus 5 GGs and 2 GPs. For you, that's lvl4 units out of the gate. Basically, you can produce commando infantry with your current civic settings and a barracks. 5 GGs + 4 xp (civic) + 3 xp (barracks) = 17 xp. Aggressive = C1. 17 xp gets you 4 promos, so C4 + Commando. If Zara has railroads actually built it might be worth building a few of these and pillaging stuff in his heartland; be careful because they can't take cities without siege support, so aren't as useful as you'd hope. Commando tanks can if you have enough of them...but I would rather get C2 CR3 tanks instead, if you want tanks. Stack 4-5 infantry together and be careful to not pillage the roads/railroads, just the improvements. If you target health/happy resources inside his BFC's you can severely hurt him. I say those because he'll defend them with units, an the ones outside the BFC will have forts and CG defenders, which suck to attack. In general, it just may not be worth the extra effort at this point.