Which region should Nabokov draw in the history of literature? I feel that he is quite marginalized, as if he is neither an American writer nor a Russian writer.

I checked the history of world literature. Nabokov is a Russian-American writer and an American immigrant writer in the 20th century. In fact, he has not been marginalized. The marginalization you mentioned is in China. Few people know him in China. It was because of his Lolita that it was made into a movie. In fact, he is a very important writer in the history of western literature. The American immigrant writers he represented in the 20th century are a very important page in the history of literature.