Hopefully this helps. If not, let me know so I can answer it properly.
Answer:
B. maintained the nation's equal number of slave and free states.
Explanation:
Missouri Comprise of 1920 was a law passed by the Congress of the United States in which Maine was admitted as a frees state into the Union and Missouri as a slave state. The issue of slavery has divided the northern and the southern states and admission of a new state attracted both the abolitionist and pro-slavery sides to exert greater influence by increasing their domain. The comprise therefore was a meantime framework to avoid direct conflict but it not settled and exploded in the form of Civil war.
While there was slavery in the past in European nations as well, it wasn't as rampant as it was in the United States where there were a lot of plantation owners who also owned multiple slaves and whole families at times - before this was made illegal during the US civil war.
