Although Tristan is commonly placed in the Arthurian stories, in the earliest versions of the story neither Arthur nor any of his traditional court appears. It is therefore no surprise that they are absent from the 2006 movie starring James Franco and Sophia Myles. Absent, too, is a consistent storyline in the literary tradition, which is why the interpretation can be such a loose one.
The movie takes a legend which has never been chronologically placed and puts it in the years immediately following the withdrawal of the Roman Empire. This has the advantage of adding political motivations to the plot and therefore complexity.
However, that decision pressures others. There is the omission of the dragon slaying in order to make the plot look historical. Having put it into a context, there is a need to add in political factors. Mark, in tradition a powerful king who was never challenged after his marriage to Isolde, is made into a leading rebel in a loose confederation. He spends the movie competing with his peers over leadership and dealing with the Irish king’s intrigues. By the time all these consequences have played out, the movie is nothing more than a romance set in the past which has borrowed the names of two famous lovers to make it more attractive to a potential audience.
Even here in that regard it fails miserably. The Ireland of the fifth century was comprosed of hundreds of semi-independent kingdoms, were politically incapable of controlling Britain. For their part, the British had no kingdoms before the last couple decades of the fifth century and the Germanic not for another fifty years after that. One can go into the problems of the plot overwhelming the romance, the swords being inaccurately long, and the social dynamics of the war-band being misrepresented, but for the historian the contriving of subplots at the expense of the original story is enough to render the whole thing not worth watching.