In my current game both Congo and myself have a 98% CB against one another and since both began increasing I have been trying to cancel key treaties such as free trade, immigration, labor force, and Criminal extradition. Each time I get the same response that Congo doesn't want to cancel the treaties. The decision for me to stop a treaty on my side of the table shouldn't require a response from the other country. This should be changed in 2020.
My second issue is that the AI countries continue to build a military far greater than its population/economy can support. A secondary affect of this is that the AI countries begin spilling large numbers of troops into neighboring countries with whom they have a land treaty. Each country, regardless of treaties, should keep their troops in their area! The only caveat to this is if a neighboring country requests a "specific" number of troops to beef up their defenses. By specific I mean that if Country A has awesome AD and Artillery and Country B has no AD and limited Artillery then Country B could request Country A to provide support.
Back to the CB issue: In my same game I am allied with Tanzania and have a large number of troops positioned to deal with any Congo DoW. The problem is that Congo also has an alliance with Tanzania and many of its troops are spilling into and mixing it up where my troops are deployed. Diplomatically, Tanzania and I have great relations with minor CB against one another. I believe the CB between Congo and Tanzania is probably low as well, however Congo has become more and more aggressive and is on the brink of war with me! I continue to provide Tanzania with monthly stipends of many resources and money, not to mention the over-generosity of my technology gifts to Tanzania. These acts along should align Tanzania with me enough that it would side with me diplomatically and began cancelling treaties with Congo, boycotting resources, etc.
On Diplomacy, I would like the AI to be able to suggest, accept, and decline diplomatic actions with the Player. Such actions as allowing the AI to build on my territory and vice-versa, for instance roads or railroads, airports or naval ports, and especially power and resource producing industry. Once built the item belongs to the host country not to the one building it.
In closing, I do not understand why I cannot cancel a treaty between my country and the AI, especially if that country's CB continues to increase! I also do not believe that inducing a boycott against an AI country does anything special - even though you know they have to be purchasing such items.
ps. even with this small issue, this game is great!