Manifest destiny is defined as the belief that the united states should own everything from the atlantic ocean to

a

canadian boarder

b

mexican boarder

c

pacific ocean

d

the appalachian mountains

D - Appalachian Mountains

Explanation:

These places are the closest to the United by which they can rule

2018 means 2018 ce or common era

there have been other eras too including bce, which included way more years.