It always seemed odd to me that the Federation had a treaty/alliance with the Cardassians but not the Romulans. They make a treaty, and then the Cardassians capture and torture one of Starfleets best captains.
Thanks to DS9 I do love the Cardassians, but in the early days they were shown quite consistently to be untrustworthy and it isn't until DS9 that we see sympathetic Cardassian charachters-Natima Lang, Tekeny Ghemor, Garak. Of course this is an issue with portrayals of "the enemy" as untrustworthy and brutal, but Romulans don't really have the same problem.
Sure, Romulans are constantly portrayed as back stabbing and sneaky (and it gets tiresome honestly), but we've seen sympathetic portrayals of Romulans since TOS. The Romulan captain defeated by Kirk admits they could have been friends in another life. Spock's Romulan love interest is portrayed as quite an admirable woman. They are enemies, but ones we can understand.
TNG does even better. We have Bochra, Admiral Jarok, N'Vek. We meet the Romulan underground. We have the moment of mutual acknowledgment and the hope for better relations at the end of The Chase. Romulans and Starfleet alike seem to want their conflict to end DS9 doesn't really have many Romulans, but those we do have are seen as potential allies, even if you do have to watch your back around them a bit. Voyager shows us a sympathetic Romulan scientist who tries to help the Voyager crew.
It seems a shame that the potential for a mutually beneficial treaty with the Romulans was never really explored. If the Federation can sign a treaty with Cardassians, why are the Romulans so different?










