I believe the battle of Antietam was the one that convinced England to keep out of it.
Two men could have ended the war long before it did end. General Lee, probably the best warrior since Alexander the great, if he had chosen to fight for the union the war wouldn't have lasted a year.
That posturing poltroon, McLellan, blew it when he failed to chase Lee's army down and finish them off after Antietam. He was as useless as a trap door in a canoe.

I was thinking just yesterday that on that date in 1066, October 15, a gang of my ancestors invaded England with Wm the conqueror, and today I was reading the thread on Gettysburg, and was reminded that my great, grandfather was in the 15th Maine during that time. Of course, the 20th Maine got all the credit, mostly because they earned it. My grandfather ended up in Australia looking for gold or opals. Anything to avoid a real job.