Bill asked in a comment about the possibility of a British intervention in the American Civil War. Most of the research on that topic by professional historians has shown that had almost no possibility of happening given the high levels of anti-slavery sentiment in the British public of the 1860s. Remember that the British government had outlawed slavery in their empire in the 1830s. So there is almost no possible scenario for a British intervention in the American Civil War. Had a British government had tried that, popular opinion against the Confederacy would have brought that government down.
On the other hand, the French had a real potential to intervene. The French did not have an economic interest in Confederate cotton, but instead the French government under Napoleon III had a very ambitious expansionist policy and a fair amount of domestic problems. A blunted United States would have allowed greater French expansion in the Americas, and a war would have taken public attention away from French domestic issues. Remember that the French did intervene in Mexico in the 1860s. So a French intervention was a far more realistic possibility.
Long ago I noted that on the Volley and Bayonet Yahoo Group. In response, Greg Novak came up with this order of battle and rules for a possible French intervention in the American Civil War: