In American colleges, we have separate courses for "American literature" and "British literature." If literature were apolitical, we would not distinguish literature by national origins. But we do, proving that politics is a part of even rather traditional literary studies.
Furthermore, this means that writers in English that are not from America or Great Britain are often excluded from the canon. Regardless of merit, they are excluded for reasons of national identity (i.e., political reasons).
Literature is political. When you look at how we study it, it is quite obvious.