Seventy years ago, on March 1, 1945, Franklin Roosevelt assured a war-weary nation that a new era of international peace and democratic government was at hand. The accords signed just weeks earlier at the Yalta Conference, he told Congress, laid the foundation for postwar cooperation between the Soviet Union and the democratic West.

“Never before have the major Allies been more closely united—not only in their war aims but also in their peace aims,” Roosevelt said. He went on to predict “the end of the system of unilateral action, the exclusive alliances, the spheres of influence, the balances of power, and all the other expedients that have been tried for centuries—and have always failed.”

Whatever the president’s political objectives, he knew this statement to be false. For 11 days during their meetings at Yalta in the Crimea, the “Big Three”—Roosevelt, Winston Churchill, and Josef Stalin—had argued intensely about their spheres of influence in the postwar world. Their aims were hopelessly at odds. The ideological divisions that would characterize the Cold War were already painfully apparent.

The debate over the fate of Poland—raised in seven of the eight plenary meetings—laid bare the political and moral gulf separating the democracies from Stalin’s Russia. “Poland had indeed been the most urgent reason for the Yalta Conference,” wrote Churchill in Triumph and Tragedy, “and was to prove the first of the great causes which led to the breakdown of the Grand Alliance.” Within days after Yalta, promises of a free, independent, and democratic Poland were betrayed, as the Soviet Union tightened its grip on Eastern Europe.

FDR’s role in the political debacle following Yalta continues to be debated. The presence of the Soviet Army in Eastern Europe, the perceived need for Stalin’s help in the war against the Japanese, the desire to tether the Soviet Union to a newly created United Nations, the massive casualties sustained by the Russians throughout the war—all of these, his defenders argue, limited the president’s choices.

That may be so, but these claims evade a deeper problem—a deficit of political and moral courage. In the years leading up to the Second World War, Roosevelt had kept America militarily enfeebled and morally indifferent: an isolationist democracy unprepared to fight a major conflict without grasping for help from an aggressive, totalitarian state.

Once the United States forged a formal alliance with the Soviet Union in the war against Germany, it was inevitable that Stalin would demand the “fruits” of his victories in Eastern Europe. “It is permitted in time of grave danger,” FDR opined, “to walk with the devil until you have crossed the bridge.” He would have done better to recall another old maxim: “He who dines with the devil had better have a long spoon.”

Instead, Roosevelt’s performance at Yalta assured Poland’s Communist enslavement.

The Nazi invasion and subjugation of Poland in 1939, of course, had triggered the Second World War. With Germany’s defeat near, the American and British negotiating teams went to Yalta determined to compel the Soviets to agree to a new Provisional Government in Poland—reorganized “on a broader democratic basis”—to replace the Communist puppets installed in the fog of war. After that, democratic elections would be held. “Honor was the sole reason why we had drawn the sword to help Poland against Hitler’s brutal onslaught,” Churchill said, “and we could never accept any settlement which did not leave her free, independent, and sovereign.”

But Stalin and his key negotiator, Vyacheslav Molotov, assailed the political integrity of Poland at every turn. After initially agreeing to a new Provisional Government, they insisted that the Communist Lublin Committee remain in control. Roosevelt was conciliatory. “The United States will never lend its support in any way to any provisional government in Poland which would be inimical to your interests,” he assured Stalin. He then assented to Stalin’s demand.

The Soviets also agreed to “free and unfettered elections” in Poland—but reneged on an earlier plan to allow international election observers into the country. Again, FDR backed down. The transcript of their deliberations includes this exchange:

FDR: I want this election in Poland to be the first one beyond question. It should be like Caesar’s wife. I did not know her but they said she was pure.

Stalin: They said that about her but in fact she had her sins.

FDR: I don’t want the Poles to be able to question the elections.

Molotov: We are afraid to leave this phrase in [about election observers] without consulting the Poles. They will feel that it shows a lack of confidence in them. It is better to leave it to the Poles.

FDR: Why not leave this for the foreign ministers and talk about this tomorrow?

Convinced that he needed a Polish settlement to secure domestic support for his dream of a United Nations, Roosevelt instructed his aides to delete the offending provision for election observers. This last stroke guaranteed that Poland would be denied a free, fair, and democratic election for the next 45 years—until the collapse of the Soviet Union.

At one point during the negotiations, FDR claimed that the differences between Russia and the United States and Britain over Polish independence were “largely a matter of the use of words.” British Foreign Secretary Anthony Eden was appalled. In his memoir, The Reckoning, Eden summarized the U.S. president’s frame of mind: “He was deluding himself.”

How, indeed, could FDR put his trust in Stalin’s word? As historian Fraser Harbutt reminds us in Yalta 1945, the Poles had endured the Red Army’s invasion and ruthless occupation of 1939-41; the forcible deportation of 1.5 million of their citizens to the Soviet Union, where thousands died in labor camps; and the Katyn massacre, in which Soviet functionaries executed Polish military officers and secretly dumped their bodies into mass graves.

Stalin had already drenched his own country in blood rather than permit democratic elections there. He had extinguished political opposition through show trials, purges, and assassinations. He had engineered man-made famines claiming the lives of millions. All of this was known when the Allies met at Yalta.

Why would FDR try to convince Americans that a paranoid and murderous dictator such as Stalin would allow “free and unfettered elections” in any country he controlled?

FDR’s ego offers a partial explanation: He believed he personally could persuade Stalin to behave more like a sensible, liberal democrat, a progressive like himself. “I believe he is truly representative of the heart and soul of Russia,” Roosevelt had said after the Tehran Conference, “and I believe that we are going to get along very well with him and the Russian people—very well indeed.”

The president’s health made matters worse. Gravely ill after entering his fourth term of office, Roosevelt probably heard only half of what was said during the Yalta meetings. “The British diaries and memoirs bristle with complaints,” writes Harbutt, “especially about the president’s performance.” His physical decline—he would die on April 12—seemed an outward manifestation of his astonishing lack of insight and resolve at a moment of international crisis.

The brief against FDR is not only that he willingly delivered the Polish people into Stalin’s hands, but that he gave moral legitimacy to this deliverance, creating a counterfeit narrative of the character and ambitions of “Uncle Joe.” Thus he told Congress: “I am convinced that the agreement on Poland, under the circumstances, is the most hopeful agreement possible for a free, independent, and prosperous Polish people.”

Roosevelt could not have believed it. He offered the American people a seductive falsehood—a deception based upon a delusion underwritten by political ambition and personal vanity. This is how democracies decline. This is the deep tragedy and the bitter lesson of Yalta.

Joseph Loconte is an associate professor of history at the King’s College in New York City and the author of A Hobbit, a Wardrobe, and a Great War: How J.R.R. Tolkien and C.S. Lewis Rediscovered Faith, Friendship, and Heroism in the Cataclysm of 1914-1918 (forthcoming).