Right, I can imagine this might interfere too much with the game, that is if an arms trade feature involved an unlimited amount and all types of weaponry (Nukes would obviously be ruled out). But this could really be a simple additional feature of modern indirect warfare in DoC, involving few types of offensive weapons as mentioned above and limited amounts for both buyers and sellers. No defensive weaponry could be sold (evidently the arms industry does not sell manpower, not yet). Unit donations themselves are limited, sometimes civs will refuse your generosity after a certain amount has been donated and the gift option remains shaded, probably for the same reasons you seem to have in mind, like maintenance costs... Limiting the interference of an arms trade feature with the rest of the game: Keeping this arms trade feature to extra units, very limited in time, (a modern age tech opening arms trade), quite hard to obtain (building a national project) and limited amounts would guarantee only the top three or four civs would really ever be able to use it. In most cases, none would be able to, except the willfull human player (like circumnavigating the world's oceans). Even then, limited numbers for buyers would keep the arms trade as an auxilliary strategy, unable to radically change a status quo, say 4 to 6 air and naval units, and a few tanks and missiles for each buyer civ. Seller civs would immediately disqualify as buyer civs (as opposed to the slave trade), since the minimum amount of units necessary to sell units would be the threshold above which you and AI civs can't buy any foreign units. I would see it actually as a stabilizer...if a superpower wants to keep on stacking units he'll only be able to produce them, but a minimum could be secured through trade for everyone. And why not make the seller civ participate in the maintenance, to avoid an undesirable bug of bloating weak civs with useless weaponry for your own profit... Most of all, this would concern extras only. Like missionaries or the religious superbuildings (cathedrals, mosques, etc.) it could almost work like this: Above 12 units of a certain type, a civ having completed the "Halliburton/Kalashnikov" project can sell 1 in every 2 additional units produced, with a limit of 10 units sold abroad and not yet destroyed. If at worst the buyer's army turns against the seller's army, I reckon this ratio requirement would prevent it from being a serious destabilizer. Aid and development issues for the modern era in DoC: Doc allows all kinds of options for indirect warfare and military aid when your modern army allows you to reshape world borders, by donating units, bringing civs back to life (great!) that respawn with strong armies, entering alliance wars to get OB agreements, etc. But : 1) Weak civs get weaker during the modern age (they often bare the brunt of DoC conflicts) yet desperately keep trying to produce hyper expensive units. Now that vassals break away more easily from their masters, their problems as weak nations get only worse, as they need unattainable amounts of shields to produce a reasonable army. Thus independence stops short of any strategy. Vassals often turn back to their former masters, or to new ones on a whim, like a russian frigate anchoring near Congo for example: playing Brazil lately I saw Congo going from French (historically inaccurate but reasonable) to Russian in a couple of turns! 2) Acquiring a limited army through trade could help solve this issue of stagnating weak civs, and also justify new vassal ties for recently independent civs, through improved relations with the buyer state and potential master. It seems more logical that in the modern age (not before) a weak state would agree for vassalage once a generous military deal has been made, rather than for techs or just out of fear (given that a weak civ's fear of a menacing power should find a rival's protection to soothe it). And you can't whisk that civ to your cause and influence if it hates you in the first place, whatever the insane offers you're prepared to give away. You definitely can have interesting, sometimes brilliant games in the modern era, but these weaker nations you and top AI civs are bound to use and abuse during modern times for indirect warfare often turn out desperately useless and dumb. I noticed this happens especially when I give a weak civ loads of cities to control, usually within its historical area. I may build all its infrastructures, give it dozens of workers, loads of cash, defensive units to calm its military production urges, it'll just keep producing defensive units and simply stagnate as if stunned. Leaving the arms trade issue aside, donating units could make the recieving weak civ react positively (bonuses for relations, production shifts to necessary "civilian" improvements, etc.). I would even suggest a separate special bonus regarding relations determined by military cooperation (donating army units, workers, etc.). Maybe a "+4 We hate your guts but we'd be toast if you weren't around" which summarizes the attitude of many US "friends" since 1945... I'm going way beyond my initial point, but I suggested selling weapons because I also often find myself wanting in the modern age to improve ressourceful and less ressourceful areas of the world I can't occupy directly and which remain sterile...and being able to pilot their development, namely by relieving them from immediate military needs through arms trade for example would mean in my mind a more intense general gameplay, and new opportunities. Wouldn't be great to see Anglo US relations turn out in DoC from "worst enemies" to indefectable allies or make it even a special US UHV ?... Once again I probably don't realize that this feature would bring about too many complications (and a mindwreck for programming, dunno!), but my point is that in DoC you couldn't do a lot more harm as a human player to stagnating weak AI civs during the modern age (and only the modern age) than leaving them to other predators and their own useless production rates for the weakest ones. Selling them limited numbers of weapons could be one way to make you win them back to your cause (bonuses for good relations, easier to maintain similar civics, etc.), whatever the cost for you and them, as long as it brings positive results for you!