One similarity is that both libraries were founded in the 1800s. The Library of Congress was founded in 1800 exactly, and La Biblioteca Nacional de Mexico was founded in 1867. Additionally, another similarity is that both were founded by their respective governments in order to establish one place with the majority of the country's information in it. As such, it's often impossible to check out books at these libraries, since they hold precious documents to the nation's history.
