McPherson explains why the American Civil War proceeded without foreign intervention. He outlines several factors that shaped British policy regarding the Civil War, identifying the actions of Union and Confederate navies as the most important factors.

The first action was the Trent Affair of 1861, initiated when Charles Wilkes fired on the British Trent to capture two Confederate envoys headed to Europe. Although Wilkes was initially praised by the American government and public for the capture, the perceived disrespect to the British Royal Navy prompted the threat of an Anglo-American War unless Lincoln were to apologize and release the captives. Lincoln acquiesced because the Union could not fight two wars simultaneously, and Lincoln’s acceptance gained pro-American sympathy among the British public. 

The second action was the Union blockade of the Confederate coast. Initially a challenge for the Union Navy, the blockade became effective by 1862, and Britain was inclined to respect the 1856 Declaration of Paris, which held that blockades were binding if effective. The Confederates claimed to European powers that it was merely a paper blockade, but they were ultimately forced to admit the blockade’s effectiveness, given the shortage of cotton that was affecting European economies.