At the first gathering of the “Big Three” Allied powers in the wake of Germany’s defeat in World War II, there was “no bubbling overflow of talk at luncheons and dinners in the intervals between the appointed meetings, as there had been at their earlier summits,” writes historian Herbert Feis. The presence of a common enemy and a formidable common task—vanquishing the Nazi war machine—had drawn the Soviet Union into a powerful “Grand Alliance” with her sworn capitalist enemies, the United States and Great Britain.

But now, Roosevelt, the charming patrician who had so effectively served as buffer between the loquacious and combative Churchill and the gruff, cryptic Stalin, had died. His replacement was his former vice president, Harry S Truman. Unfortunately, the haberdasher-turned-politician from Missouri had been kept almost entirely out of the picture on war policy in general, and on the delicate matter of negotiations with the Russians in particular. Truman had no previous experience with foreign affairs beyond his exemplary service as a World War I captain of artillery.

Now, in July 1945, in the quiet Berlin suburb of Potsdam, it was time to construct a new Europe and a lasting peace, anchored on the principles of national self-determination, free elections, and rule of law—at least, that’s what had been agreed to in principle at Yalta, where Roosevelt, Stalin, and Churchill had last gathered. Trouble was, as Feis so quaintly put it, now the victors’ “thoughts were brushed by the cold snow of mutual distrust and dislike.” The vast differences in ideology, history, and worldview between East and West were making it devilishly hard to get much agreed beyond the seating arrangements for the deliberations—and, of course, that the Nazi high command should be vigorously prosecuted for their heinous crimes.

As the war in Europe drew to a close, Truman’s advisors had explained at length to their new boss that Stalin had tipped his hand, subtly and not so subtly, that he would continue to talk the talk of democracy and self-determination even while his vast security and espionage apparatus worked methodically to infect all Europe, West as well as East, with the virus of communism. The Red Army and the notorious NKVD—the secret police—had already eliminated pro-Western, pro-democratic political parties in the former German satellites of Bulgaria and Romania.

Churchill vehemently protested against Soviet crackdowns in those countries, and elsewhere in Eastern Europe. The British prime minister strenuously objected as well that official British and American observers’ movements in those countries were tightly restricted by Soviet agents. Stalin calmly called these charges “fairy tales.” But of course, the accusations were anything but.

At Potsdam, Truman and Churchill haggled at length with Stalin over the details of what mattered most: the future of Germany. The Western leaders had come to believe that the best protection against a revival of German aggression lay in restoring the German people to a prominent place in the political and economic life of Europe—after a long period of reform and re-education. Stalin, for his part, preferred partitioning the country into a number of loosely connected states, essentially bereft of industrial, as well as military, capacity. And he seemed inclined to repeat the mistake of Versailles by saddling draconian reparation payments ($20 billion) on the backs of a prostrate German people—and transferring most of the country’s remaining industrial base east to the Soviet Union.

Meanwhile, as the negotiations ground on tediously in the July heat, Stalin became more thoroughly convinced than ever that his Western counterparts were determined to deny the Soviet Union at the bargaining table what it had earned on the battlefield.

Nonetheless, after some prodigious behind-the-scenes work by the allies’ foreign ministers and their diplomatic staffs, some agreements were finally reached. In the end, the Russian strong man assented to the Western view that Germany should be treated as a single political and economic unit, though the nature of its new national government was put off until another day. “The German people,” as the official Potsdam Declaration issued at the conclusion of the gathering put it, would “be given the opportunity to prepare for the eventual reconstruction of their life on a democratic and peaceful basis.” To fulfill this directive, the country would be temporarily divided into American, Soviet, British, and French zones, each zone to be administered by an army of occupation, led by a commander in chief.

Insofar as it was possible, these armies would enforce uniform general policies of occupation, namely the “five D’s”: demilitarization, denazification, democratization, de-centralization, and de-industrialization. The Soviet Union would be permitted 10 to 15 percent of the industrial base from the Western zones, in exchange for agricultural products badly needed by the German population in the West.

Reluctantly the Americans and British accepted the Oder-Neisse line as the temporary border between Poland and Germany in the West, which meant the transfer of a considerable part of eastern Germany to Poland, and the forced repatriation of at least three million Germans into the Western zones. To soften the blow, Stalin promised that the Polish provisional government would hold “free and unfettered elections as soon as possible on the basis of universal suffrage … in which all democratic and anti-Nazi parties shall have the right to take part,” and that the Western press shall enjoy “full freedom to report to the world upon developments in Poland.”

Finally, Stalin confirmed Russia’s agreement to enter into the Pacific War three months after Germany’s surrender, and supported a declaration issued by the U.S., Britain, and China threatening the Japanese with “prompt and utter destruction” if it did not surrender immediately and unconditionally. (The Soviet Union did not sign the document because it had yet to declare war on Japan.) The threat was no bluff. As Truman famously revealed to Stalin during the deliberations at Potsdam, the United States had just detonated the world’s first atom bomb.

The three heads of state presented the Potsdam Declaration to the world as a sound and enduring plan for world peace, but their words, it seemed to many observers at the time, lacked conviction. And not without good reason.

The Potsdam plan for peace began to fray around the edges even before the formal declaration was published and distributed. By 1947, the vicissitudes of great power politics had rendered the blueprint for peace hammered out there pretty much irrelevant, except as a reference point in trading accusations of violations of the spirit and the letter of the agreement itself.

In the event, there would be no “joint” reconstruction of Europe, no collaboration between East and West in rebuilding a war-ravaged Europe. What emerged instead, and rather quickly at that, was a protracted and bitter geopolitical struggle between the two superpowers and their allies, soon to be known the world over as the Cold War.

In blatant violation of the Declaration, the Soviet Union rapidly reconstituted the German Communist Party in the Eastern Sector of Germany, which took its orders directly from Moscow, and placed its members in almost every meaningful position of political and administrative authority. Leading members of pro-Western parties in the eastern sector were efficiently rounded up, thrown in jails, deported, or killed.

Stalin was laying the foundation for an entirely separate, East German nation state, modeled not on the best traditions and values of the German people, but rather on those of the Soviet Union.

This process was duplicated in Poland, despite the strident protests of members of the former Polish government in exile (the “London Poles”) that had done so much to aid in the defeat of Hitler in the West, and the large and passionately anti-communist Polish community in the United States.

Just four days after the conclusion of the conference in Berlin, the United States dropped the atomic bomb on Hiroshima. After a second bomb devastated Nagasaki, Japan surrendered. “Hiroshima has shocked the whole world,” Stalin told his scientists, as he initiated a crash program to produce a Soviet weapon of even greater power. “The [strategic and military] balance has been destroyed … that cannot be.” Because of the bomb, Stalin had been denied what he dearly coveted: a role in the defeat—and more important, the occupation—of Japan.

Immediately the Soviet Union began to take aggressive, highly provocative measures to enhance its strategic position vis a vis the West. Stalin refused to withdraw the Soviet army from oil-rich Iran, despite having promised to do so by the end of 1945 at Potsdam. Then came outrageous Soviet demands for territorial concessions from Turkey, along with naval bases that would have given the Soviets effective control over the strategically vital Dardanelles straits.

When a U.S. aircraft carrier steamed in the direction of the Dardanelles, Stalin backed down on his demands for bases and territorial concessions from the Turks. After the Americans brought the Soviet army’s occupation of Iran before the new United Nations—its first international crisis—Stalin stalled for a while, and then quietly withdrew the troops.

Why were the Soviets violating their agreements and constantly seeking to expand their influence and power westward by subversive means? American diplomats seemed at a loss to explain what was going on with their wartime ally. A brilliant junior American foreign service officer who had studied Russian history in depth, George F. Kennan, thought he knew. He spelled it out in an 8,000-word telegram, written from his desk in the Soviet embassy in Moscow in February 1946.

Soviet intransigence wasn’t the result of Western provocation. Rather, Soviet leaders had to present the outside world to their people as hostile, for it provided an excuse for repression at home, the domination of Eastern Europe, and the great sacrifices the Soviet people were required to make so that Stalin could further expand his already considerable military and industrial assets.

To expect reciprocity for diplomatic concessions from the Russians would be fruitless. The Soviets would continue to try to expand their sphere of influence whenever and wherever they could. What was needed, as Kennan later put in an essay in Foreign Affairs based on the famous “Long Telegram,” was “long-term, patient but firm and vigilant containment of Russian expansive tendencies.” Therefore, wrote Kennan, American policy must be centered on “the adroit and vigilant application of counter-force at a series of constantly shifting geographical and political points, corresponding to the shifts and maneuvers in Soviet policy.”

Truman—indeed, the entire U.S. foreign policy establishment—found Kennan’s analysis compelling, to say the least. And they acted on it. On March 12, 1947, Truman appeared before a joint session of Congress to make his case for standing up to communist subversion. “The foreign policy and the national security of this country,” he claimed, were involved in the crises then confronting Greece and Turkey. Greece, he argued, was “threatened by the terrorist activities of several thousand armed men, led by communists.” It was incumbent upon the United States to support Greece so that it could “become a self-supporting and self-respecting democracy.”

The “freedom-loving” people of Turkey also needed U.S. aid, which was “necessary for the maintenance of its national integrity” in the face of pressure for concessions from the Soviets. The president declared that “it must be the policy of the United States to support free peoples who are resisting attempted subjugation by armed minorities or by outside pressures.” And so the Truman Doctrine was born.

A few months later, much to the Soviet Union’s chagrin, Truman initiated a massive reconstruction of Western Europe on America’s dime. The Marshall Plan, named after then-secretary of state George C. Marshall, was designed as a response to the continued economic crisis in Western Europe, which Truman and Marshall feared would cause despair and instability, leading to the spread of Communism.

Pravda, the most prominent Soviet newspaper, labeled the Marshall Plan a “Truman Doctrine with dollars.” Stalin saw the Truman Doctrine and the Marshall Plan as but further evidence of “capitalist encirclement.” His view was elevated to an article of faith in the Kremlin, and so it remained until the Cold War began to sputter to an end in the late ’80s.

The idea of Western encirclement of Russia’s sphere of influence, of course, has been vigorously revived in the past several years by Vladimir Putin in an attempt to justify his own expansionist designs in the Ukraine, as well as the costs of those designs borne by the Russian people in the form of Western sanctions.

As one might expect, given the trajectory of events traced above, Potsdam proved to be not only the first “Big Three” peace conference after the defeat of Germany, but also the last. Today, 70 years later, the conference is best remembered as a noble but tortuous effort that did less to chart the path to peace than to mark the beginning of an entirely new conflict altogether.