what arguments did W VA and NH from MA make to make their new states?
Don’t know what most of east CA doesn’t form their new state either, and while they’re at it maybe the 3 counties in the south east of my state Miami, Broward and Palm for their new state too
West Virginia separated from Virginia at the start of the Civil War. Being an area largely without slaves and with strong Union sentiments, they made no "argument", they just did it.
When the Virginia legislature voted on an "Ordinance of Secession", the delegates from the northwestern counties voted roughly 2-to-1 against it. Then, when the ordinance was ratified by a popular vote, the northwestern counties again voted against it -- by a roughly 2-to-1 margin.
Whereupon a convention of the northwestern counties was called in Wheeling in June, 1861 and they voted to secede from Virginia and apply for statehood in the Union. Statehood was granted in 1863.
West Virginia’s statehood was an act of conquest by a foreign power. New Hampshire was a colony before independence.
New Hampshire was never a part of Massachusetts. I think you're confusing it with Maine, and that partition was approved by the Massachusetts legislature.
As for West Virginia, when Virginia joined the Confederacy they formed their own legislature loyal to the Union. That legislature was recognized by Congress, voted to partition, and Congress approved.