The British would not in fact just for pragmatic reasons have entered the war on the side of the South--for all sorts of reasons, including the strong anti-slavery forces in the British citizenry--even many who themselves were economically dependent on the South. Again, history is complex. But combined with visceral emotional reaction when national honor or sovereignty was seen as attacked-- (and by an uncouth Mammon- chasing upstart-- (the North), it could have happened.   Highest danger points were the "Trent" affair and the time when it looked possible that the North, fearing the Laird "rams" could break the blockade of the South--naval men on both sides of the Atlantic felt this-- would send US Navy ships up the Mersey to destroy the "rams" at anchor.