Historically some nation's traded with thier enemies so to say it's good and realistic to restrict trade to this degree is untrue.
Even if in real life,enemies did not trade with each other,neutral countries certainly did trade with each other. The way Bytro has made it,we cannot even trade with nations with Share Map. We have to be in the same coalition,and in most maps,coalitions can only have 3 members. THREE. That means a coalition member only has two trade partners in most maps. And what about games that do not allow coalitions? I am currently playing a game as France and I need oil. I want to ask Morocco for oil,but I notice that I cannot propose a resource trade. In that game,Coalitions are disabled. That means that nobody can trade resources and units in that game.