Earlier quoted context omitted.
A civil war. Right. Completely displaying your ignorance of the region's history.
The history where for the last 400 years the were part of the same country and share close history for 2000 years and only a tiny amount of time they were fully separated. They speak essentially the same language (often the very same) and use the same national origin story and the Russian Orthodox Church was literally representing people from both sides of the border. There are tons of families and other connections…
The "national origin story" (unless you mean the 1917 Revolution) is nothing like how the two countries were created.
Mexico and the US have "tons of families and other connections over the (sic) boarder as well."
The reason the elites treated the border between Ukraine and the Russian Federation as meaningless was because ex-Soviet cronies were running Ukraine to plunder its assets. Until the Maiden Revolution, these cronies were basically stooges controlled by Moscow.
The current conflict (2014 to now) is nothing like a civil war. Moscow uses some proxy forces from the Luhansk and Donetsk oblasts, but the majority of forces are from the Russian Federation. They control everything, supply all the equipment and determine goals and objectives. If you were to remove the Russian forces from these two oblasts (as well as Crimea and Zaporizhzhia) these proxy forces would collapse immediately.
Oh and regarding England and Scotland, well, many Scots would like to leave the UK. That wouldn't be a civil war either, but an independence movement. A civil war would be the more like the Hundred Years war...