What's the difference between British and American literature and English language literature?

From the perspective of major setting, English language and literature, like Chinese language and literature, are two major majors (undergraduate majors), commonly known as English Department. British and American literature is a specialized course or branch of English language and literature, just as ancient China literature is a branch of Chinese language and literature. At the postgraduate stage, foreign literature in Chinese department and foreign literature in English department can both major in British and American literature. Geographically speaking, British and American literature is British and American literature, and English language and literature has a wide range, so long as it is written in English, it can be counted. For example, Russian Nabokov wrote Lolita in English, which is also regarded as English language and literature.