When you trade resources, wether in diplomacy or on the stock market, you instantly get it. But to make CoW more realistic, they should make it where you either send trucks, planes, or ships to the country that you're trading with to give them the resources. (Units would be sent to the country's capital). Also, when you're shipping off goods, they can be hijacked by another country and they steal the resources. There would be something about it in the news, and it would cause war. If you're sending a plane, it can be shot down, and if you send a truck, you have to have right of way with the country that your truck is passing through.