Why were levees built along the Mississippi River in 1900?

New settlers adopted aggressive flood-control tactics to protect their new settlements from inundation. Rather than only settling those lands less susceptible to overflow, the new frontiersmen also reclaimed lands well within the floodplain and constructed levees to protect them.

the catholic church withhold people's access to the bible during the middle ages.

people could go to church and listen to the teachings, but it was absolutely forbidden to own and/or read the books of both the old and new testaments. it was also prohibited to translate the books (which where originally in biblical hebrew) to any other language.

this was done so the church could remain in control of what their teachings were and to enhance their importance and power, while also being able to judge people's actions through information that was unavailable for the general public.