I've never heard of unionists threatening to bomb London if the British withdraw. That's pretty crappy republican propoganda. Threaten to bomb Dublin yes. Threaten to defy and disobey a United Ireland government yes. And they are not bluffing either.
Just remember that the "visiting transplants" as you insultingly call them have been in Ireland longer than your people have been in Northern America.
Not true, 3 slave states remained in the Union. S Carolina voted to become an independent country and not be a part of the Confederacy. 4 counties in N Carolina voted not to join NC's secession and never did. There was hardly uniform agreement in Dixie.
Most in the South knew they had no chance, especially without foreign help.
The bottom line is that imperial monarchy-driven colonial attitudes and greed brought the Brits to Ireland, created the oppression there and they have no one but themselves to blame if London gets bombed.
How does Britain find itself a heartbeat away from verstehen und sprechen sie deutch and can't get its Irish neighbor to help? Perhaps being a better neighbor and America wouldn't have had to bail them out twice with our blood and treasure that would never have been created in a monarchy.
Pre-1640?
Doubt it.