The money you invest in the agreement is lost. That`s not necessarily a bad thing – if you can go to war with someone, they`ll lose the money they could have used to defend themselves. Investments in research agreements are lost if they are broken. That`s why you should never go to war with your research partners if you can help him — because you lose both. I made a research agreement with an AI at Civ 5, and when it was half over, he attacked me. Has that money disappeared for both of us, or can we take it back once I teach him a lesson? According to Wikipedia, the main opponents of the computer will sometimes use this strategy. GPT as mentioned BlueRaja is a good achievement safely. Opening borders is also good trade or just about anything that pays off on several twists and turns, including your excess strategic resources. You think it`s a horrible idea to arm the enemy at your doorstep, but as soon as they declare war on you, there will be 1 thing out of 2: let`s say you trade iron for gold in Montezuma just before he declares war on you… 1) He already had more reserve irons than swordsmen/catapult/etc. on the ground, which means that the excess iron you gave him was useless, but he has now funded your defense/fun budget. 2) Montezuma has actually been able to increase his maximum number of units (iron) on the trade, but now that your iron stock is cut, Montezuma will have a lack of iron, which results in all his swordsmen/catapults/etc will have a combat punishment until he can return to the black numbers. In addition, it has now funded your defense and fun budget.