The Anaconda Plan
The Anaconda Plan is a decision that is made during the American Civil War by the USA against the Confederate States of America. If it is not used during the civil war, it can technically be used in a hypothetical later war. The results of this decision increase the war exhaustion of the CSA by 0.05. It is recommended to use it especially if you are beginning to lose the war, but it is useful in any situation.
It is possible to enact it, when CSA makes a blockade on at least 80% of USA's provinces. It is very likely that CSA does so during the civil war.