Sylvia Engdahl’s 1970 Enchantress From the Stars is the first of the two Elana novels, also the first of five Anthropology Service novels.
The Federation is vast and powerful; it is also a good neighbor. It is not inclined to try to fix other cultures (Special Circumstances, cough cough). The Federation takes non-interference seriously enough that its very existence is a secret from less developed star-faring powers. Protecting pre-industrial worlds like Andrecia from imperialists (like the Empire) would therefore seem to be impossible.