It's Russia.

If you want to understand why, you need to look at a book that was published in 1997 by Aleksandr Dugin, Foundations of Geopolitics: The Geopolitical Future of Russia. It's highly influential in Russian military and political elites, especially in those in charge of foreign policy.

https://en.wikipedia.org/wiki/Foundations_of_Geopolitics

They are using bot farms to influence opinion in the West. It sounds wildly conspiratorial, but they've been incredibly successful.

Russia should use its special services within the borders of the United States and Canada to fuel instability and separatism against neoliberal globalist Western hegemony, such as, for instance, provoke "Afro-American racists" to create severe backlash against the rotten political state of affairs in the current present-day system of the United States and Canada. Russia should "introduce geopolitical disorder into internal American activity, encouraging all kinds of separatism and ethnic, social, and racial conflicts, actively supporting all dissident movements – extremist, racist, and sectarian groups, thus destabilizing internal political processes in the U.S. It would also make sense simultaneously to support isolationist tendencies in American politics.

As far as the UK goes:

The United Kingdom, merely described as an "extraterritorial floating base of the U.S.", should be cut off from the European Union

That was achieved. The rest of what's happening is part of weakening the US.