As a student of history you know the thought of the South conquering the North is ludicrous, right?
The entire notion of the south taking up arms against their countrymen was ludicrous....but they did anyway.
And you know that the thought of North Korea conquering the US is ludicrous, right?
And yet, if North Koreans nuke even one of our cities, even one like Nancy Pelosi's home town, they could expect to be glassified in return.
Now consider some foreign military force which took over a third of our states, and threatened half those remaining.
What damage would we do to them today?