The decline began in the 1880's as industrialization increased.
The answer is A, is it sort of "commoditized" the products made with it, allowing the products to become cheaper and mass produced.
Answer:
Its members waged an underground campaign of intimidation and violence directed at white and Black Republican leaders. Though Congress passed legislation designed to curb Klan terrorism, the organization saw its primary goal–the reestablishment of white supremacy–fulfilled through Democratic victories in state legislatures across the South in the 1870s.
The reason why vernacular literature eventually became the preferred way to produce books is because the "vernacular" was something that the majority of people could understand in terms of written language--meaning that a publisher and writer would make much more money printing in this language.