Foreign enlistment in the American Civil War was largely dominated by the Union, which was far more successful in attracting international volunteers. Nonetheless, thousands of immigrants and mercenaries served with the Confederacy.
Although the Union Army's largest foreign-born contingents comprised Irish- and German-Americans, regiments such as the 79th New York Highlanders, originally formed in the 1850s, consisted completely of descendants of Scottish immigrants before accepting Irish, English and others into its ranks during the early years of the war. It should be noted that these immigrants had been living in the US for years prior to the war and did not come to this country to fight in the war.
Communication difficulties, especially in Union regiments, were a constant problem in divisions made up of varied nationalities. Such divisions included volunteers from Germany, Ireland, Italy, Poland, and other European countries. One regiment, in particular, was made up of officers and soldiers from 15 different nations, and the commanding officer's orders had to be translated in seven different languages. Major General Franz Sigel had his orders translated from his native German to Hungarian, for his officers, then to Reports to him then had to be translated in English for the rest of his command and finally to German again, when Sigel received reports.
The US, especially in the North, had received a large influx of European immigrants in the 1850s, due to people leaving Europe to avoid the ongoing wars and rebellions there. Europe had been in the midst of a pro-republican transformation with people such as Garibaldi, in Italy.
Many British citizens from the colony of Bermuda, especially from the coloured (a term in Bermuda used to designate anyone not entirely of European heritage) population, fought for the Union, either in the United States Navy or the United States Army. Among others, these included Robert Tappin (who had previously served in the US Navy from 1863 to 1864), John Wilson and Joseph Thomas of the 31st Colored Infantry Regiment, John Thompson of the 26th Colored Infantry, Wate O. Harris, of the 6th Coloured Infantry, and George Smith. The best known of the coloured Bermudians to serve in the Union army was First Sergeant Robert John Simmons of the 54th Massachusetts Infantry Regiment, who had previously served in the British Army in Bermuda. Simmons was to die of wounds following the Second Battle of Fort Wagner, on the outskirts of the Bermudian settlement of Charleston, South Carolina, where most of the weapons run through the blockade from Bermuda were landed. Other British citizens who were active in the war included numerous Irish emigres, who served in large numbers on both sides. Many of these Irish veterans took part in the Fenian raids on Canada after the war, and Britain strengthened the defences in Bermuda against the possibility of similar raids there and against a feared punitive invasion of the colony by the United States.
Thousands of pre-war immigrants served in the Confederate Army, which had its own Irish Brigade and Polish Legion, as well as several German and Mexican divisions. These units were composed of men who had lived most of their lives in the USA. The most notable volunteer division comprised descendants of people from various European countries then living in Louisiana, under the command of French Major General Count Camille Armand Jules Marie, Prince de Polignac.
The war was to split the British population as well as American, in both the mother country and her colonies. In Britain, those who benefited from the sale of war materials and supplies to the Confederacy, whose cloth factories were dependent on the supply of American cotton, or who admired the vaguely aristocratic political heirarchy of the Southern states, were set against abolitionists, at least until the Trent Affair. The conflict was even greater in colonies that were nearer to the field of battle. Located 640 miles off Cape Hatteras, North Carolina, Britain's oldest remaining colony, Bermuda, had been settled accidentally in 1609 as an extension of Virginia, with which it would long retain close ties of blood and trade, and from which Charleston and the Province of Carolina had been settled under William Sayle in 1670. Bermudians had also provided important cadres of skilled settlers to the settlement of other southern colonies, including Georgia and Florida. These close ties had led Bermudians to sympathise with the rebels during the American War of Independence, supplying them with ships and weapons in exchange for exemption from the embargo of the Continental Congress on trade with colonies not in revolt. American independence led to Bermuda's designation as the headquarters and dockyard of the Royal Navy's North America and West Indies Squadron, with a heavy buildup of regular British Army units for both the defence of the colony, and for launching potential expeditions and campaigns throughout the region, as was demonstrated during the American War of 1812, when most of the Atlantic ports of the United States were blockaded by the fleet based in Bermuda, and the Chesapeake Campaign, which included the Burning of Washington, was launched from the colony. During the American Civil War, St. George's, Bermuda was the primary harbour from which British and European war material was smuggled into the South aboard blockade runners (also built in Britain). Cotton travelled in the reverse direction in payment. Although it had been perceived in the South as an enemy, supporting abolition, before the war, Britain nearly entered the fray effectively as an ally of the Confederacy following the Trent Affair, building up forces in Canada to either defend against a Union attack, or to launch an invasion of the northern states, while preparing the naval and military forces in Bermuda to launch an expedition intended to capture New York. Many British citizens took part in the war in the Confederate forces, including Henry Wemyss Feilden, who resigned his commission in the British Army to become an officer in the Confederate Army, and William Watson, who served as a sergeant in the 3rd Louisiana Infantry before crewing blockade runners. In Bermuda, the close historical ties with the South, as well as the enticement to profiteer from the war by supplying the South, meant that the Confederate agent operated openly from the Globe Hotel in St. George's, while the US Government's consul was attacked in the street and had his flagpole cut down on the 4th of July. Many Bermudians earned fortunes handling supplies to the South, or, like Thomas Leslie Outerbridge, crewing blockade runners. Another prominent volunteer was the Scotland-born, Captain William Watson.