A civil war in the UK would not benefit the US, neither a hard border with the EU/Ireland (i.e for trade).
>> Asked to name his biggest competitor and foe globally, the US president said there were "a lot of foes" and named Russia and China among them, but the first on his list was the EU.
https://www.rte.ie/news/us/2019/1201/1096402-gfa-congress-br...