What impact would British and French involvement in the civil war have had?

The United Kingdom of Great Britain and Ireland remained officially neutral throughout the American Civil War (1861-1865). It legally recognized the belligerent status of the Confederate States of America (CSA) but never recognized it as a nation and neither signed a treaty with it nor ever exchanged ambassadors. Over 90 percent of Confederate trade with Britain ended, causing a severe shortage of cotton by 1862. Britain financed blockade runners that sent munitions and luxuries to Confederate ports in return for cotton and tobacco. Top British officials debated offering to mediate in the first 18 months, which the Confederacy wanted but the United States strongly rejected.

The British elite tended to support the Confederacy, but ordinary people tended to support the United States, the Union or "the North". Large-scale trade continued between Britain and the US. The US shipped grain to Britain, and Britain sent manufactured items and munitions to the US. Immigration continued into the US, with many Britons volunteering for its army.[quantify] British trade with the Confederacy fell over 90% from the prewar period, with a small amount of cotton going to Britain and some munitions and luxury goods slipped in by numerous small blockade runners. They were operated and funded by British private interests. They were legal under international law and caused no dispute between the US and Britain.[1]

The Confederate strategy for securing independence was based largely on the hope of military intervention by Britain and France. That never happened because the US threatened war, which would have cut off much of Britain's food supply. A serious diplomatic dispute erupted over the "Trent Affair" in late 1861 but was resolved peacefully after five weeks.