In 1861, The London Times Got It Right

The contest is really for empire on the side of the North, and for independence on that of the South, and in this respect we recognize an exact analogy between the North and the Government of George III, and the South and the Thirteen Revolted Provinces.

---The London Times, November 7, 1861, quoted in Jeffrey Rogers Hummel, Emancipating Slaves, Enslaving Free Men: A History of the American Civil War, Chicago and La Salle, Illinois, Open Court Press, 1996, p. 168

Hummel notes earlier on p. 168:

Britain was the neutral country that mattered most, and slavery was a key issue affecting its reaction.  Lincoln, however, had made clear that the war was for the preservation of the Union only.  He promised not to interfere with slavery in the states, and many Union commanders during the early campaigns returned runaways to their southern masters, in compliance withe the Fugitive Slave Law.  As a result, the foreign antislavery movement was reluctant to throw its weight behind the Union, and many Britons openly sympathized with the Confederacy.