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Hundreds of letters congratulating Abraham Lincoln on his inauguration poured in from all over the world in the spring of 1861, but one in particular caught the eye of Secretary of State William Henry Seward: it was from the oldest surviving republic in the world, “the Most Serene Republic of San Marino,” addressed to the new president of a much younger and most troubled republic facing secession and civil war.

Seward brought it to Lincoln’s attention. Though it took several weeks for him to respond, Lincoln was greatly moved by the letter. It stirred him to see the national calamity now facing his own country as part of a much grander question: what future, if any, did republican democracy have in a world beset by slavery and tyranny?

San Marino State Tourist Bureau

Perched high in the Apennine Mountains on the Adriatic side of the Italian peninsula, San Marino occupied (and continues to occupy) about 24 square miles of rocky escarpments. Less than a thousand families inhabited the land, most of them clustered inside San Marino’s city walls or in scattered villages.

San Marino’s history as an asylum from persecution and despotism stretched back to its very founding in 301 A.D., when a Christian named Marinus fled the persecution of the Romans to seek refuge in the mountainous enclave. Eventually a small colony of Christians formed, taking its name from their founder, later to become Saint Marinus. Thanks in part to their country’s formidable geography and in part to their consistent political neutrality, the San Marinese were able to resist conquest by aggressive neighbors for centuries: the Duke of Montefeltro next door in Urbino, the Pope in Rome, French armies under Napoleon I and, in 1861, the newly united Kingdom of Italy.

But an even more striking aspect of the country’s history was its political structure. Since about 1300, San Marino had been governed by the same body of elected representatives, the Capitani Regenti. In 1600 San Marino promulgated a written constitution that codified its institutions and laws, a document still in force in the 21st century. San Marino remains the oldest constitutional republic in the world, almost twice as old as the runner up, the United States.

San Marino and the United States were members of a very small club: in the mid-19th century republics were an endangered species. Amid the ruins of dozens of revolutionary republican movements that erupted in Europe between the French Revolution in 1789 and the revolutions of 1848, few genuine republics endured, and the tide of democracy was giving way to the imperialist ambitions of kings and emperors. Only Switzerland, a federated republic modeled after the United States, and tiny San Marino upheld the republican ideal in Europe. Across the Atlantic, most of the Spanish American republics had either fallen under the despotic rule of military caudillos or were torn by warring factions of conservative landowners and clergy against liberal republicans.

But much more so than San Marino, since its founding the United States had been admired among liberals in Europe and elsewhere as a pioneer in the “republican experiment,” a model — imperfect and unfinished, to be sure — but nonetheless a working example of how a free, self-governing people might live. Now it was descending into a fratricidal war that threatened to prove the whole experiment in self-government a failure, a risk that its leaders were all too aware of. In his Inaugural Address earlier that March, Lincoln argued against the abstract principle of secession as a threat to the fundamental workings of a self-governing republic; to allow aggrieved minorities to secede every time they did not like the outcome of an election or some act of government was “the essence of anarchy” and the ruin of a self-governing society. And he knew what that failure would mean in the international arena: America stood as one of the few lonely beacons of the republican ideal, the “last best hope of earth” as Lincoln would later put it.

It’s no surprise, then, that both Seward and Lincoln took interest in the letter from the Regent Captains of San Marino. The letter had two columns, with perfect Italian on one side, and imperfect but clear English on the other. “We have wished to write to you in our own hand and in English, although we have little knowledge and no practice in the language,” the regents explained. “It is a some while since the Republic of San Marino wishes to make alliance with the United States of America in that manner as it is possible between a great Potency and a very small country.”

Indeed, the two countries faced similar political straits as well. San Marino’s recent troubles went back to 1849, when it offered asylum to Giuseppe Garibaldi and his army of Red Shirts who were fleeing from French and Austrian troops after the fall of the revolutionary Republic of Rome. Pope Pius IX controlled the Papal States surrounding San Marino and the Austrian Empire controlled Venice to its north. To the Pope and the Hapsburgs, Garibaldi and his “red republicans” were akin to revolutionary terrorists. Somehow Garibaldi then escaped San Marino, leaving Austrian soldiers to kick in doors looking for men and arms left behind.

Library of Congress

By 1861 the Austrians still controlled Venice, but the realm of the Papal States had shrunk to the area immediately surrounding Rome. The previous year Garibaldi and his Red Shirts conquered much of the area to the South of San Marino in the name of King Victor Emanuel II. San Marino became surrounded by a newly united kingdom that proclaimed its existence as a nation in March 1861, precisely as the regents wrote to Lincoln proposing an “alliance” between fellow republicans in a perilous world. Whether the new monarch would appreciate San Marino’s role in protecting Garibaldi, let alone respect its right to exist as an independent republic, was unsure — hence the plea to Lincoln. “As we think not extention of territories but conformity of opinions to procure friendly relations,” the regents wrote, “so we are sure you will be glad to shake hands with a people who in its smallness and poverty can exhibit to you an antiquity from fourteen centuries of its free government.”

“Now we must inform you,” the letter to Lincoln continued, “that to give to the United States of America a mark of high consideration and sincere fraternity the Sovereign Counsel on our motion decreed in its sitting of 25th October … that the citizenship of the Republic of San Marino was conferred for ever to the President pro tempore of the United States of America and we are very happy to send you the diploma of it.”

The regents then alluded to the recent difficulties of their sister republic across the sea: “We are acquainted from newspapers with political griefs, wich you are now suffering therefore we pray to God to grant you a peaceful solution of your questions. Nevertheless we hope our letter will not reach you disagreeable, and we shall expect anxiously an answer which proves us your kind acceptance.”

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The letter from San Marino was addressed to Lincoln in New York, which the Regent Captains must have assumed was the capital of the United States. It probably arrived in Washington in mid-April, when Lincoln was about to experience even more “political griefs.” But on May 7, amid all the turmoil, Lincoln and Seward (both signed the letter) found time to graciously accept the “honor of citizenship” from San Marino.

“Great and Good Friends,” the reply to San Marino began, “Although your dominion is small, your State is nevertheless one of the most honored, in all history. It has by its experience demonstrated the truth, so full of encouragement to the friends of Humanity, that Government founded on Republican principles is capable of being so administered as to be secure and enduring.”

Lincoln’s letter then turned to America’s troubles: “You have kindly adverted to the trial through which this Republic is now passing. It is one of deep import. It involves the question whether a Representative republic, extended and aggrandized so much as to be safe against foreign enemies can save itself from the dangers of domestic faction. I have faith in a good result” — a thought the president would place at the center of his Gettysburg Address, still two and a half years in the future.

Note: An earlier version of this article made a reference to “the mid-18th century” instead of “the mid-19th century”; that has been corrected.

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Sources: The state public archives of San Marino provided copies of the correspondence with Abraham Lincoln and the minutes of the October meeting of the Regent Captains; Abraham Lincoln to the Regent Captains of the Republic of San Marino, May 7, 1861, National Archives; John M. Taylor, “William Henry Seward: Lincoln’s Right Hand Man”; Charles Bruc, “The Republic of San Marino.”

Don H. Doyle is a professor of history at the University of South Carolina and a public policy scholar at the Woodrow Wilson International Center. He is the author of “Nations Divided: America, Italy, and the Southern Question” and is writing about a book about the international context of dimensions of the American Civil War.