I think that it would be B.trade
The correct answer is increase in industrialization.
Due to the technological advancements of the mid-late 1800's, Americans started to rely more on industry rather than farming. Working in a factory rather than a farm had its perks. People who worked in a factory had guaranteed wages, whereas in farming the amount of money a person makes is dependent on several different factors like the amount of people who want to buy your products, climate, location, etc.
Pueblo grants were used to establish new settlements and communities in new Mexico.
