The interaction between man and nature is a major theme for Coleridge. It's painted all over "Kubla Khan," as we go from the dome to the river, and then from the gardens to the sea. Sometimes he's focused on human characters, sometimes on natural forces. In fact, it's difficult to get away from this theme in this poem. Think of this tension as a tug-of war between humans and their temporary constructions (buildings) and the seeming permanence of nature.
Coleridge describes many natural scenes in this short poem, and gives limited details about the human objects. Since he gives us only a sketchy picture of the man-made pleasure dome, he focuses our attention on the power and importance of the natural world.