What was the Cold War—and are we headed to another one?

As World War II dragged to an end in 1945, the leaders of the “Big Three” allied powers—the United States, Soviet Union, and Great Britain—met in Potsdam, Germany, to hash out  terms to conclude the bloodiest conflict the world had ever seen. The great powers split Germany into occupation zones, recognized a Soviet-backed government in Poland, and partitioned Vietnam, monumental decisions that shaped the postwar global order. The talks were meant to forge a lasting peace, but within 18 months, a Cold War began that lasted more than four decades.

One of the most important moments at Potsdam was not captured in a memo or proclaimed at a press conference. Late in the conference, U.S. President Harry Truman took aside Soviet premier Joseph Stalin to share some explosive news: The U.S. had just successfully tested a weapon of “unusual destructive force.” It was a nuclear weapon capable of destroying entire cities, the most dangerous and powerful armament the world had ever seen.

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Within weeks, the U.S. used the atomic bomb to force Japan’s surrender. With a devastating and proven weapon in its armory, the U.S. suddenly had the upper hand among the powers who were allies in the war. What followed was a dangerous struggle for supremacy between two superpowers, the U.S. and the U.S.S.R., that lasted until the collapse of the Soviet Union in 1991.

Though the two nations were technically at peace, the period was characterized by an aggressive and costly arms race; bloody proxy wars fought across Latin America, Africa, and Asia; and competing bids for world dominance between U.S.-led capitalist governments and the Soviet-led communist bloc.

The Cold War lasted nearly half a century. Here’s a look at why it began, how it escalated, its legacy today—and why some analysts think another Cold War is already underway.

Why’s it called the Cold War?

The term “cold war” had existed since the 1930s, when guerre froide was used in France to describe increasingly fraught relationships between European countries. In 1945, shortly after the United States dropped the atomic bomb on Hiroshima and Nagasaki, British writer George Orwell used the term in an essay that explored what the atom bomb meant for international relations.

The atom bombs killed more than 100,000 Japanese citizens, unveiling a destructive power so terrifying that Orwell predicted it would discourage open warfare among great powers, creating instead “a state which was at once unconquerable and in a permanent state of ‘cold war’ with its neighbours.”

Orwell’s prediction of a “peace that is no peace” came true as seeds of distrust between the former allies grew.

Okay, so how did the Cold War begin?

The U.S.S.R. had borne the highest number of military and civilian casualties in the war—an estimated 24 million—while liberating huge swaths of Eastern Europe from Nazi control. Soviet leader Josef Stalin was dissatisfied with the postwar division of Europe, which he felt didn’t fairly reflect his nation’s contribution.

In the U.S., diplomat George Kennan outlined the Soviet Union’s growing distrust in the 1946 “Long Telegram,” as it is now known. Kennan warned that the U.S.S.R. was illogical and insecure and would not cooperate with the West in the long-term. In response, Washington began to pursue a policy of “containment” to prevent the spread of Soviet ideology and influence.

The U.S. soon got an opportunity to flex its new policy. In 1947, Britain announced it would withdraw aid from Greece and Turkey, which were both battling communist uprisings. President Harry Truman seized the occasion to ask Congress for funds to assist both countries, establishing what became known as the Truman Doctrine—the principle that the U.S. should support countries or people threatened by Soviet forces or communist insurrection. Stalin saw the move as the opening shot of a shadow war.

The term “Cold War” became a shorthand to describe the ideological struggle between capitalism in the West and communism in the East.  American journalist Walter Lippmann popularized the term in a series of articles in 1947 as nations chose sides in the standoff.

Why was NATO created?

The U.S. wasn’t alone in worrying about Stalin’s push to extend Soviet influence westward and bring other states under communist rule. In 1948, the U.S.S.R. backed a communist coup in Czechoslovakia and launched a blockade of west Berlin, which had been divided into occupation zones controlled by communists in the east and capitalists in the west.

To demonstrate a united front, the U.S. and its allies formed a transatlantic mutual defense alliance known as the North Atlantic Treaty Organization, or NATO. On April 4, 1949, the U.S., Canada, Belgium, Denmark, France, Iceland, Italy, Luxemburg, the Netherlands, Norway, Portugal, and the U.K. signed a treaty agreeing that “an armed attack against one or more…shall be considered an attack against them all.” 

The U.S.S.R. responded by creating a defensive alliance of its own. Signed in 1955, the Warsaw Pact included the Soviet Union and seven satellite states, including Poland and East Germany, reinforcing the ideological and military barrier between Eastern and Western Europe that Winston Churchill had dubbed the “Iron Curtain” in a 1946 speech.

How close did the world come to nuclear war?

As the two sides faced off across that Iron Curtain, the U.S. and U.S.S.R. engaged in an arms race, pouring trillions of dollars into accumulating nuclear arsenals.

The U.S. had an advantage at the start of the arms race. But once the U.S.S.R. built its own nuclear arsenal, the two sides were at a standoff over “mutually assured destruction”—the idea that if either side attacked, the other would retaliate, unleashing apocalyptic consequences for both parties.

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Both countries had missile defenses pointed at one another, and in 1962, the Cuban Missile Crisis brought the countries closer to the brink than any other event in the Cold War. The U.S. detected Soviet missile bases and arms in communist Cuba, just 90 miles south of Florida. Demanding they be removed, President John F. Kennedy declared that a strike on U.S. territory would trigger an immediate nuclear strike on the U.S.S.R.

The threat of imminent nuclear war hung over nearly two weeks of tense negotiations. Finally, the U.S.S.R. agreed to dismantle its weapons facilities if the U.S. pledged not to invade Cuba. Behind the scenes, the U.S. agreed to remove nuclear weapons from Turkey; that agreement did not become public until 1987. 

Nevertheless, both sides’ nuclear arsenals continued to grow exponentially. By the late 1980s, the United States had an estimated 23,000 nuclear weapons to the Soviet Union’s 39,000.

How else was the Cold War fought?

Over more than four decades of Cold War, the U.S. and Soviet Union waged multiple proxy wars across the globe. In the Korean War, the Vietnam War, and other armed conflicts, the superpowers funded opposing sides or fought directly against communist or capitalist militias. Both sides funded revolutions, insurgencies, and political assassinations in Latin America, Africa, Asia, and the Middle East.

The U.S. and Soviet Union also jockeyed to prove technological dominance in a 20-year Space Race. The Soviet Union scored first with the 1957 launch of Sputnik-1, the first artificial satellite, while the U.S. was first to send a man to the moon in 1969. Only in the mid 1970s did the two nations begin to cooperate on joint missions.

(50 years after Apollo 11, a new moon race is on.)

How did the Cold War end?

By the mid 1980s, life behind the Iron Curtain had changed. Democratic uprisings were percolating in Soviet bloc nations, and the U.S.S.R. itself struggled with economic and political chaos. The U.S. and U.S.S.R. forged a more open relationship, even brokering a nuclear treaty in 1987 that eliminated a class of particularly dangerous ground-launched missiles from the nations’ arsenals.

By 1991, the Soviet Union had lost most of its bloc to democratic revolutions, and the Warsaw Pact was formally dissolved. Mikhail Gorbachev, the last leader of the U.S.S.R., opened his country to the West and instituted economic reforms that undercut institutions that relied on nationalized goods. In December 1991, the U.S.S.R. was dissolved into separate nations.

What does all this mean now?

The U.S.S.R. is gone, and nuclear arsenals have dramatically decreased thanks to nonproliferation treaties between Washington and Moscow in the 1980s and 1990s. In recent decades, the U.S. and Russia have cooperated on a number of global issues, including Afghanistan and the war on terror.

But the Cold War still affects modern geopolitics. Both nations still have divergent geopolitical interests, large defense budgets, and international military bases. NATO still wields political power and has grown to include 30 member states. The alliance now stretches to Russia’s borders and includes former Soviet states and Warsaw Pact members, such as Poland and the Baltic States. Since the 1990s, Russia has seen the eastward expansion of NATO as a threat to its security.

Tensions between Russia and the West reached a new high point following the February 2022 Russian invasion of Ukraine, which had applied to take the first steps toward NATO membership in 2008, before a new president shelved the plan two years later. Some commentators have likened the current crisis to the beginnings of a new Cold War.

(Follow Ukraine's 30-year struggle for independence with this visual timeline.)

Is a 21st-century Cold War already being waged? It remains to be seen. Though historians say the decisions at Potsdam set the stage for a long post-World War II rivalry, we may not recognize the beginnings of a new Cold War until it’s visible in history’s rear-view mirror.