As Prussia the only problem with taking Rhineland was the incredibly annoying incessant offers to trade it away from Spain, France and the UP, at least 1 per turn.
Eventually I swapped it with Spain for Lombardy (borders my Venice and protectorate Italian States), Cuba and New Mexico. Cuba gave me an impregnable foothold in the Americas which, since I had no navy and was at war with GB, was a big boost. Gave New Mex to eventual enemies Poland to waste money on in exchange for $. Next turn I took back Rhineland and wiped out the French, then knocked off the 3 Iberian provinces. Couldn't be bothered to build a navy to get to Sardinia so got peace with Spain for Hispaniola and $.
So far the only swaps I have done are extracting them for peace or swapping and then taking back what I swapped away. With no reputation system it's full steam ahead for swapping and taking back next turn!

I have tried a few times to buy a province for 120k but got rejected each time.
I really wish the AI would stop spamming me with really stupid offers of 1 tech for a 10k province or 1 crappy province for 3 good ones of mine. I am actually worried that in my haste to get rid of them I will accidentally press Accept!
Bookmarks