Why is washington, d. c. included in the southeast region?

There are no fixed regions available to make Washington D.C. in another region. It is where it should belong and if there was a law to change the location (if possible), then you could change the location. (in the northeast, midwest, etc.)
Hope this helps! :)

It is the doctrine that the us had the right and duty to expand throughout north america. it just means they believed they had the right to expand westward and they did! they stated with the 13 colonies and then they kept moving gaining different territories throughout the years

D. latin america followed by africa