Learn Spanish (Spain): ¿A usted le interesa la historia?

In this sentence, we are using the formal "you" (usted). Because verbs like interesar work like the verb gustar (literally meaning "history is interesting to you"), we need an indirect object pronoun. For usted, that pronoun is le. If we were talking to a friend, we would use te.

If we already have le, why do we also say a usted?

It is actually optional, but very common! The pronoun le can mean "to him," "to her," or "to you (formal)." Adding a usted clarifies exactly who we are talking to so there is no confusion. It also adds a nice touch of politeness and emphasis.

Why is the verb interesa in the "he/she/it" form if we are asking "you"?

Verbs like interesar and gustar work backwards compared to English. The true subject of the sentence is la historia (history), not "you." Literally, the sentence is asking, "Is history interesting to you?" Since la historia is a singular thing, the verb takes the singular form interesa.

Why is there a la before historia? We don't say "the history" in English.