Refers to a theory developed and popularized in the 19th century to provide a rationale for the united states to expand from the atlantic ocean to the pacific ocean.

in 1803 the louisiana purchase took place, doubling the size of the country. by 1840 almost 7 million americans had migrated westward in hopes of securing land and being prosperous. the belief that settlers were destined to expand to the west is often referred to as manifest destiny.

explanation:

c, they united with once

answer; the period of time known as the middle ages;

the correct answwer is d