In mid-July 1862, Confederate envoy John Slidell met secretly with French Emperor Napoleon III at the latter’s private vacation home in Vichy, far from others who might uncover their plot. Dominant in Louisiana politics, Slidell was the South’s most effective diplomat, and he understood Europeans enough not to discuss slavery. Instead, he emphasized why the Confederate cause would be in the interests of France—whose government detested liberal values and the French Revolution, limited press freedoms, and even outlawed displays of the red liberty cap. Speaking with the emperor, Slidell proposed an alliance. If the French would use its navy to lift the Union’s blockade of Southern ports and recognize the South, the Confederate States would offer a generous trade deal and give France free cotton. Beyond these perks, the emperor recognized why a Confederate victory was in his interests. The failure of the United States would prove the dangers of republicanism and democracy, thus bolstering his autocratic rule and undermining his liberal opponents. Meanwhile, a Union victory threatened his puppet monarch in Mexico, Maximilian I, whereas a Southern buffer state would protect France’s strategic interests in the Americas. Slidell and Napoleon III’s long and friendly conversation gave the envoy hope that the French Empire would soon recognize the South, force the Union to negotiate, and end the war, which would have had dramatic consequences for world history.

Don H. Doyle, who was a professor of history at the University of South Carolina, recounts this episode in The Cause of All Nations: An International History of the American Civil War. While most histories of the Civil War naturally focus on the drama in America, Doyle explains how the conflict fits into broader world history and how events abroad affected the war. As his narrative describes, both the Union and Confederacy made critical diplomatic mistakes, which today can teach policymakers important lessons, particularly on public diplomacy.

For the Confederate States, recognition from foreign powers would have ended the war in its favor because the United States could not confront the rebels and a united coalition of great powers. Meanwhile, European liberals accepted that regions could secede from larger entities and form new nations—as Greece and Belgium had already done, and as many hoped Hungary, Ireland, and Poland would do soon. During this age of nationalism, it was unclear which large countries would remain united and which would divide, and many did not see the United States as a true nation with a group of people with a strong common identity. So Southerners could have tried to convince Europeans that they were fighting for national self-determination because they were culturally distinct from the self-righteous, hypocritical descendants of Yankee Puritans. If Confederates’ public diplomacy campaign focused on issues like their national uniqueness and free trade instead of slavery, the European public may have sided with their cause, even if liberals hoped the South would eventually implement emancipation. Yet the Cornerstone Speech by Confederate Vice President Alexander Stephens in March 1861, which explained that slavery was the reason for secession, undermined the South’s message when foreign audiences read it. Though Slidell emphasized Europe’s strategic interests instead of slavery, other Southerners would over the years insist on defending slavery and their racist ideology to European audiences, who rightly concluded that if not for slavery the South had no reason for rebellion.

Yet the North also made public diplomacy mistakes because it would not commit to ending slavery. Instead, it made legalistic arguments about the US Constitution and legitimate authority. European liberals were unimpressed. If the Union fought only to preserve its dominion without emancipation, they viewed the cause as unjust and the North akin to an illiberal empire.

While the government in Washington was unwilling to say it fought to end slavery, writers, ministers, professors, intellectuals, and other Europeans tried to convince audiences on both sides of the Atlantic that the war was for liberty. For example, Agénor de Gasparin—a French liberal Protestant who lived in self-imposed exile after the French Revolution of 1848—argued that the war was one for liberty in both America and Europe and that this issue was the main issue for Christian ethics. Mary Louise Booth in New York translated his book, which was widely read in the US and spurred debate.

In addition to European writers explaining why the Civil War was to free slaves and promote liberty globally, a multitude of foreign-born fighters, including one of Doyle’s ancestors, joined the Union cause. He gives evidence, including letters, that shows how many of these men believed that fighting the South would bring liberty to their homeland, and on their marches they would sing “La Marseillaise,” a song Napoleon III banned. While the largest groups came from Germany and Ireland, many others also fought and died. Exact numbers are unknow, but Doyle estimates that around 43 percent of all Union forces were either immigrants or the sons of immigrants, and about a quarter of the Union army was foreign-born. If the Union had relied only upon Americans born in the US, the Confederacy would have likely won.

Throughout the book, the failed revolutions of 1848 loom in the background, and the Civil War should likely be understood in the global context of conflicts that began in Europe decades earlier. Those uprisings across continental Europe influenced many actors in the book, including the liberal writers, Union diplomats, and soldiers. For example, many Germans fled their homeland after governments there suppressed their uprisings, and they brought their liberal philosophy and politics to the North. When war began, they recognized their opportunity for a second fight, which they were more likely to win. As one immigrant explained why her son fought, “I am from Germany, where my brothers all fought against the government and tried to make us free but were unsuccessful… We foreigners know the preciousness of that great, noble gift a great deal better than you, because you never were in slavery, but we are born in it.” Meanwhile, the authoritarian governments of Europe feared a new wave of uprisings, which influenced their policy decisions.

For Doyle, the pivotal moment came in 1862 shortly after Slidell and Napoleon III discussed an alliance. While other historians point to Abraham Lincoln’s Emancipation Proclamation in September of that year as the moment when the Union’s diplomatic fortunes changed, Doyle disagrees. According to his evidence, the Proclamation made intervention more likely because European leaders feared Lincoln’s actions would inspire uprisings in their territories and cause the collapse of the cotton trade, hurting their economies. But Giuseppe Garibaldi upset their plans for intervention when he and his Redshirts marched on Rome. King Victor Emmanuel II of Italy sent the royal army to stop the advance, and near the mountain Aspromonte on August 29, two bullets struck Garibaldi, who surrendered. News of this popular figure’s imprisonment spread quickly across Europe, causing riots in places like Hyde Park, London. Meanwhile, the Union’s consul in Vienna, Heinrich Theodore Canisius, wrote to Garibaldi asking whether he would “lend us a helping hand in our present struggle to preserve the liberty and unity of our great Republic.” Garibaldi responded that despite being wounded he hoped to serve the United States, of which he claimed citizenship, because it was fighting for “universal liberty.” Newspapers in Europe and America published the Italian hero’s reply, thus connecting the popular Garibaldi to the Union’s cause at a moment when his imprisonment dominated the news cycle. US Secretary of State William Seward fired Canisius for sending the unauthorized letter, but Doyle credits this personal diplomacy for changing the Union’s fortunes. Later that month, Garibaldi wrote another letter urging Britain to reject an alliance with France against the United States. The press published it on October 3, three days before Britain learned about the Emancipation Proclamation. Doyle provides evidence that Garibaldi-inspired popular unrest in Britain caused the government to decide against intervention. Though press restrictions limited the Garibaldi news in France, Napoleon III would not act alone, so the Confederacy lost its best opportunity at international recognition.

For readers interested in foreign policy, this episode with Garibaldi and other incidents that Doyle describes offer clear lessons about public diplomacy. Governments should recognize how their messaging and actions, both at home and abroad, can influence public opinion and pressure states. Yet there are limits to this strategy. Policymakers fool themselves if they think the will of a majority of people can override a government whose support comes from a small clique. When an authoritarian is confident in his or her essential backers’ loyalty, public opinion is of little consequence, as in the case of Bashar al-Assad. The people’s will is irrelevant if the military is willing to kill them until they submit. Yet in a case like Europe during the Civil War when leaders feared 1848-style uprisings, public diplomacy can be critical, as the Union and Confederacy learned.

The South’s surrender in 1865 would have consequences for the global spread of liberalism, as Doyle explains. European authoritarians expected a Confederate victory that would prove that large liberal republics could not survive, yet Union victory showed liberalism’s viability, weakening authoritarian regimes and their narratives. In America’s immediate neighborhood, Napoleon III abandoned Mexico. Without a Confederate buffer state, the US resupplied the forces of Benito Juárez, who would defeat the Mexican Empire and, against the pleas from prominent voices, execute Maximilian I in 1867. Beyond Mexico, Doyle lists other global consequences of Union victory, including for Brazil, Santo Domingo, Peru, Chile, Cuba, Canada, Spain, Britain, and France.

Many Europeans recognized and appreciated how the Civil War affected them. After the fall of the Second French Empire in 1870 when French liberals could again show appreciation to America without government interference, they constructed a gift, first conceived in 1865: officially titled Liberty Enlightening the World, a statue in New York Harbor looking across the Atlantic and walking toward Europe with the broken chains of slavery at her feet and a beacon of liberty in her right hand.

Doyle recounts how decades later Adolf Hitler mourned the collapse of the Confederate States and complained that the Civil War destroyed a system of racial inequality. In time, a unified America that the war preserved would come to Europe and with allies liberate the continent from Hitler’s illiberal tyranny. So with a broad view of world history, the Union’s supporters abroad were right to see the conflict as one for liberty not just for America but for the world.