The first couple of stanzas in this poem are simply imagery. Coleridge describes the vision of Xanadu and introduces Kubla Khan in a very progressive tone. He describes Xanadu's environment in great detail, until line 29 where he reveals that Kubla has heard "voices prophesying war." This could be seen as foreshadowing to a potential war, where in that case the war would be considered the climax of the poem. However, Coleridge does not develop that idea any further. There is an abrupt halt in the maturation of the Xanadu paradise at line 36, which appears to be part of an incomplete stanza.
Following line 36, there is a clear change in writing from the author. Not only does he change his point of view from third person to first person, but he also changes the tone which shows that he is retreating from his Xanadu. This creates a clear distinction between Coleridge's original poem (lines 1 through 36) and what he later added on as a conclusion (lines 37 through 54). The last two stanzas can be seen as Coleridge's longing to gain his vision of Xanadu once again and complete his original work. When looking at the entire poem from that perspective, it is a complete idea. There is no need to extend the poem after the final line 54 since the author can not revive what he already lost.
It is not certain at what point exactly Coleridge was interrupted from his writing, nor is the identity of the man responsible. However, many theories have been made to answer these questions and more. It is safe to assume that while Coleridge did not have the chance to continue with his original idea of the Xanadu paradise, he still found another way to end his poem so that it could be published. As a whole, Kubla Khan can be seen as a complete poem about a man who lost his short-lived paradise.