I recently finished a campaign in which I successfully made more than 5 diplomatic deals by threatening the other nation, but did not receive the achievement "Observe Diplomatic Niceties" which states "Use diplomatic threats to good effect by making gains from five separate negotiations". I did a search and saw many other players were having the same issue and found an easy solution on how to obtain the achievement.

The easiest way to unlock this achievement, is by playing Episode II of the "Road to Independence" campaign.


The first issued mission is to make an alliance with the Iroquois Confederacy. You can use the threaten button to make the alliance, and they will always accept.


After getting the alliance, you can do this again to get a trade agreement. After you successfully get the trade agreement and the alliance, finish the turn so the threats get recorded. You can then go to the main menu, select episode II, and do this again until the achievement is unlocked. Easy!