How do I go back east if I've never been to the east? It does not make sense to return to a place you've never been.
In American English, we sometimes say up north, down south, out west, and back east when referring to directions. The words up, down, out, and back do not have any special meaning in this context, but are often used as a matter of convention. Additionally, the Eastern United States is sometimes referred to as back east.
According to this Ngram, it appears that this usage became more common in the latter half of the 19th century, began to decline between 1940 and 1970, and then became more widely used than before:
"Back east" is a west coast-ism to refer to the east coast, as a corollary to "out west". See e.g. http://www.wordorigins.org/index.php/forums/viewthread/1898/
The underlying source is the idea everyone is somehow "from" the east, and they (or their ancestors) at one point moved "out west", but if they were to return, it would be to go "back east."
Most of the settlement of the United States was done by people moving from east to west. For example, the original 13 states in the United States were along the Atlantic coast.
Yes, the Spanish also colonized Florida, Texas, New Mexico, and California, and the French colonized Louisiana -- but those are exceptions that prove the rule. In 1803 (when the U.S. purchased Louisiana), the Louisiana Purchase was of territory adjacent to and west of the United States. In the 1830s, American settlers moving west from Tennessee greatly outnumbered the Spanish-speaking colonists in Texas. In 1849, a "Gold Rush" of American "49ers" moving west similarly overwhelmed the Spanish-organized Indians around the California missions.
Most of the people who moved west during the settlement of the United States moved to areas where North literally is upstream from South. Most of the United States is in a huge basin, bounded by the Appalachian mountains in the east, the Great Lakes in the northeast, (roughly) the Canadian border, the Rocky Mountains in the west, and the Gulf of Mexico in the south. With a few exceptions, most rivers in this region flow southwest, south, or southeast. In this basin, "downstream" is toward the Gulf of Mexico (that is, toward the "South").
Sometimes "back X" can refer to a cultural or family home, even if one has never been there.
I'd love to go back to Africa
The implication is that one's culture, or "roots" are in Africa. However, this is still ambiguous as the speaker might quite rightly assume that the speaker had been there before.
There has been some similar answers to this one. I'm not an expert, I'm not even american, but if you watch this video historian Colin Calloway gives some insight as of why this might be such a common term.
I'm from the Enumclaw, WA. To my cohorts and me, "back east" basically refers to anything north of the Carolinas and east of Indiana or Ohio-ish. It does not reference people who used to live on the east coast. It's a loose geographical reference. East of the midwest and north of the south is the most common usage, but I have heard people refer to places like Chicago as back east. However, in my humble opinion that would be incorrect usage.