Border wars are border wars and need not imply full out war with the other country.
In my recent campaign I am playing Poland and at war with Prussia, Austria and the Crimean chanate (don't ask me why). Yet none of these countries sent a single unit to fight on Polish soil (on H/H). You can easily interpret it as a low intensity border war without any serious intent. In fact I can build everything I want and still have a sizeable reserve in the treasury (and I have only 4 landlocked provinces).
The point is that being in war need not imply an all out rampage and that you might be better off with your "dear enemy" than eliminating it and drawing in another nation into war with you.

This of course does not deny the short comings of the diplomacy or the gang on the human player effect. It just that you can use wars to your own advantage.