Eastern Tennessee did not border on the state of West Virginia. If you mean "southwestern Virginia" the fact is that it--and indeed much of the southern part of West Virginia as well--was actually pro-Confederate in sentiment during the War. To quote an old post of mine:
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…[O]ne should not view West Virginia monolithically. There was very strong pro-Union sentiment in Northwest Virginia, but there were also pro-secessionists in much of the area that later became West Virginia. The best study of this is Richard Orr Curry, *A House Divided: A Study of Statehood Politics and the Copperhead Movement in West Virginia* (University of Pittsburgh Press 1964).
Curry points out that it is important to distinguish between Northwestern Virginia, Southwestern Virginia, and the Shenandoah Valley. There had indeed been a time when all three of these regions had been united against the slaveholders of eastern Virginia. The goals of the West at that time had been universal manhood suffrage, popular election of the governor (and of judges, etc.), abolition of the governor's council, increased representation in the General Assembly, and an end to tax discrimination in favor of slave property. By 1830, the Valley had deserted the west, politically; and the Tran-Allegheny Southwest followed suit over the next few decades, leaving the Northwest as the only true "west." Partly, this was because slavery was taking root in these areas (especially the Valley) more than in the Northwest; also because internal improvements linked the Valley and the Southwest to the rest of Virginia.
Not only did the Northwest not get any program of internal improvements comparable to the Valley or the Southwest but such improvements as she *did* get, such as the Cumberland Road and the Baltimore and Ohio Railroad (the latter was hampered at every turn by the Virginia legislature and did not reach Wheeling until 1852) tended to link her to the North, not the South. Furthermore, the rivers of the area flowed westward into the Ohio, which encouraged trade with the Northwest, not the South. And of course slavery was not likely to flourish in a cold, mountainous area. Finally, not only did places like Wheeling become industrial centers, but they got a considerable Northern migration.
Thus far, Curry agrees with the traditional or "pro-Union" account of the origins of West Virginia. But he emphasizes an often-neglected point: West Virginia included a large number of Southwestern and Valley counties, and even Northwestern counties were not *all* against secession. He argues that the vote was about 30,000 to 10,000 against secession in northwestern Virginia but 9,000 to 4,000 for it in the other areas of the future West Virginia--which btw in terms of area (as distinguished from population) made up a majority of the state. The counties he gives as favoring secession are Logan, Boone, Wyoming, Mac Dowell, Mercer, Raleigh, Monroe, Greenbrier, Fayette, Nicholas, Clay, Roane, Calhoun, Gilmore, Braxton, Webster, Pocahontas, Randolph, Barbour, Tucker, Pendleton, Hardy, Hampshire, and Jefferson. (The present-day counties of Mingo, Grant, and Mineral did not yet exist; they were within pro-secessionist counties.)
So, while the creation of a West Virginia was logical, it was by no means inevitable that it should have its current borders. Half the counties and at least 36 percent of the population of what was to be West Virginia favored secession. (Secessionist sympathies in some counties may have eventually become stronger than the vote indicates. For example, Berkeley County, in the Valley, voted against secession, but furnished at least 400 Confederate troops as opposed to 200 Union soldiers.) A West Virginia confined to the counties which actually opposed secession would be an interesting what-if. It would have been much more Republican and much more "northern" in orientation than the West Virginia of OTL, which was Democratic for decades after the Civil War--once the test oaths were removed)--due to a coalition of ex-Confederates and ex-Copperheads.
Interestingly, at the 1861 Wheeling convention, John Carlile argued for a state of "New Virginia" that would not have included the Southwestern or Valley counties. The proper boundaries of the new state were also a subject of much debate at the 1863 constitutional convention.
https://www.alternatehistory.com/fo...inia-stick-with-virginia.331591/#post-9831104
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More generally, it is a mistake to assume that all of "Appalachia" was as Unionist and anti-secession as East Tennessee. Western North Carolina was reluctant to secede before Fort Sumter and Lincoln's call for troops; but after those events, to a much greater extent than eastern Tennessee, western North Carolina acquiesced in secession. As John C. Inscoe and Gordon B. McKinney note in
The Heart of Confederate Appalachia: Western North Carolina in the Civil War, "Yet western North Carolina's proximity to the far more prevalent Unionism across the state line did not necessarily make loyalists out of Carolina residents."
https://books.google.com/books?id=Z1ntU2N9ze0C&pg=PA95