I've heard it repeated often from many different people that the British thought about intervening in the ACW because they wanted to secure southern cotton. I find this somewhat hard to believe as the British had control of India by this time and had already begun construction of the Suez Canal in large part to facilitate trade with India. Is there any truth to this widely held idea? Did any world power consider intervening?
There were two instances in which Great Britain came closest to intervening in the American Civil War. The first was the Trent Affair of 1861. The second was the Laird Rams Affair of 1863.
The Trent Affair took place when the USS San Jacinto seized the RMS Trent, a British mail packet out of Havana. The Trent was carrying a handful of Confederate diplomats bound for Europe, where they were to represent Confederate interests. The diplomats were removed at gunpoint from the Trent, and they were imprisoned. The Trent was allowed to proceed on its journey.
This was a major diplomatic incident. The U.S. Navy had stopped and boarded a ship from a nation uninvolved in the war. It had violated international law by abducting men from that ship — remember, this very thing had been a significant factor in America's belligerence during the War of 1812 — and at the time, British interests were favoring the Confederacy.
In the United States, the captain of the San Jacinto was hailed as a hero for sticking a finger in Britain's eye. In Britain, he was a villain, a pirate violating international law. The United States and Britain traded hot-tempered messages. Britain moved additional soldiers into Canada and readied its navy for warfare.
Thanks to diplomatic action by Lincoln and Prince Albert (shortly before his death), however, tempers were allowed to cool, and each side was permitted to escape with its honor intact. The Confederate diplomats went on to Europe, where they did very little of note.
The Laird Rams affair took place in 1863 and was triggered by the radical success of the Confederate merchant raiders Florida and Alabama. In violation of the neutrality laws in place at the time, these ships were built in Britain and transferred to the Confederacy at sea. The Confederacy proceeded to arm and crew the ships for war to great success.
I'm most familiar with their campaigns through the actions of the Shenandoah, which brought the war to Alaska in 1865 when it sailed around the world and virtually destroyed New England's whaling fleet in the North Pacific. The Shenandoah fired the last shots under the Confederate flag, ending its raiding in August 1865.
But that's getting off track ...
In 1863, with the track record of the Alabama and the Florida well established, the U.S. government was taking firmer and firmer steps to prevent additional raiders from leaving Britain. The Confederacy was aided by the extremely capable J.D. Bulloch, who supervised the ordering and initial construction of two iron rams, steam and sail-powered vessels that would have been able to fight many U.S. Navy ships one-on-one at something close to even odds.
Those the U.S. government presented evidence again and again that the rams were bound for Confederate service, the British government stalled and vacillated on seizing the rams in the shipyard.
With their completion approaching in fall 1863, the U.S. government took financial action and prepared to take military action against the rams. If those ships set sail, the U.S. Navy was planning to intercept and sink them before the Confederates armed them — even if they were flying the British flag.
With American determination obvious, and thanks to some excellent diplomacy by U.S. Ambassador Charles Francis Adams, the rams never entered British service.
Now, let me take a note to mention French involvement. If anything, Napoleon III was more eager than almost any element of the British government to enter the war on the side of the Confederacy.
France was heavily involved in Mexico during the American Civil War, and its government believed that a surviving Confederacy would deny the United States the ability to exercise the Monroe Doctrine to evict foreign influences from Mexico.
Napoleon III wasn't willing to intervene unilaterally, however — he wanted British support before he took a step against the United States. That support did not come, and so Napoleon never acted against the United States.
I'm not sure if this is against the rules as I have no actual credentials for history but I'm a current us history student but here it goes:
The United Kingdom was in support of an independent south as they would have a continuous supply of cotton for there textile industry without having to deal with Union tariffs. As to how the English actually tried to help the the south was they were going to make blockade runners to break the union blockade. This fell through, however, as it would be against the United Kingdom's interests to get tangled up in a full blown dress war with the United States. Eventually the south lost all hope of European intervention with the loss of Gettysburg and other battles because no one wants to help the losing side. I will add more later as I am on mobile at the moment.
Source: My APUSH teacher and American Pageant 13th edition
A World on Fire: Britain's Crucial Role in the American Civil War, by Amanda Foreman is probably the best and most comprehensive book on this subject. It's a fascinating look at the Civil War because you never really see the war from an outside perspective. I'd recommend it.