User blog comment:Fimber/Did Uther win at last? Résumé of Merlin and the finale - The Diamond of the Day Part 2/@comment-37001937-20190114164048

"Why was Arthur destined to unite the lands of Albion and to bring back magic Why did they plan to have a sidhe queen in Camelot at Arthur's side in the first place when they were willing to let Arthur die which would have eliminated the possibility of a sidhe queen? Why did Arthur try to unite the Five Kingdoms when they were already united by Uther? Where was Godwyn when the five kings came to Camelot since he was Uther's close friend? What kindoms belonged to the Five Kingdoms at all?"

The OP answered his own question about Arthur uniting the Five Kingdoms, and I don't know why Fimber clings to the idea that Uther united them already; he clearly didn't, otherwise Morgause and Morgana wouldn't have such an easy time gathering armies and allies to try to overtake Camelot three times, and succeed two times.