Honestly, a region under a TO shouldn't be allowed to change allegiance. Seems like something you'd need actual control of the region to accomplish.
Indirik, the King of Leinster was a Petty King, on par with a Duke, and not the Royalty of England and more conventional nations.
Chenier, you're missing the point. D'hara is no Soviet Union, it is not a state hostile to Terran, has no intentions of becoming hostile to Terran, and barring the current circumstances would likely never become hostile to Terran. Which makes the analogy to Poland-Germany-USSR a poor one in comparison to Britan-France-Germany. And if you want so say fictional, well that invalidates your whole reason for posting a different analogy in the first place. If you want to go fictional well, obviously D'hara is Vermont when Babylon surrendered to it during its war with the Klingon Empire.
And who are you to say what D'Hara would or wouldn't have done?
D'Hara and Terran are NOT friends. D'Hara is, however, friends with Terran's invaders. And I dare say most D'Harans have more affinities with Phantarian than Terran. Your claim that nothing could have brought D'Hara to war against Terran is ridiculous. If it weren't for the kingdom of Saffalore occupying our forces, Alaster Kabrinski as ruler would have been more than enough causus belli.
