Given that until the 1970'S Britain seriously feared the USA, because the ruling elites of Britain feared that Democracy could only lead to chaos, it seems to me that conflict between the USA and Britain is simply underused as a seed of alternate histories. Centrum has the same ideas about democracy that the 19th century British elites had. They fear it as a door to chaos and a mask for tyranny. It seems to me that in any parallel were the ACW is occurring Centrum would bend all its efforts toward starting a war between the USA and Britain.
The main problems would be these, first,
Prussia's king hates the CSA, second, no one trusts
Louie Napoleon, third, Russia wants to embarrass Britain and the
Czar wants the Slaves freed, and sees Lincoln as the only man to do it. The Prussian King hates political revolt to begin with. That the CSA is revolting for the right to own slaves makes the king sick to his stomach. I kid you not, he is recorded as actually vomiting at the thought of the CSA! Louie Napoleon is a con man and a risk taker. He is tricky as a matter of policy and pride. The Brits know this and keep their distance. The Tsar wants to do two things, A) promote an end to slavery, the South's defeat looks good to him, and b) steal a march on Britain. The Russian Navy is basically hiding in American ports in this period. This achieves two ends. First the Brits can't blockade them in Russian ports nor can the winter. Second, Britain can't bombard US ports without starting a major European diplomatic incident.
So how do you get Centrum it's shot?