Pittsburgh ? This September the leaders of the 19 most influential nations and a representative of the European Union will gather on the banks of the Allegheny River to discuss global issues. Fifty Septembers earlier, another powerful leader traveled to Pittsburgh for conversations and speeches. The world was very different then.

This is a tale of two summits, one amid a Cold War, the other in an era of hot wars in Iraq and Afghanistan. This is a tale of two different worlds, one riven by ideological conflict, the other burdened by economic crisis.

In the contrast between these two visits — one conducted in a bipolar world, the other in a multipolar world — is the history of the world in the last half-century.

For when Nikita S. Khrushchev traveled to Pittsburgh 50 years ago to the day when delegates of the G-20 summit begin to gather here, the globe was divided between capitalist and communist. The greatest economic empire in the world was based in the steel mills of Pittsburgh, the motorcar plants of Detroit and the aviation industry of California, with new rivals springing up in hastily developed but grim industrial colonies planted on the Eurasian steppes and developed as part of the Third Five-Year Plan in the Soviet Union, a nation that no longer exists.

In Khrushchev’s time the engine of finance operated mostly on Wall Street, and maybe in the City of London, and nobody cared what the finance minister of Brazil had to say about anything. The notion that Indonesia, independent for only a decade, would be invited to a critical world summit, was beyond laughable. And Turkey, Mexico and South Africa? You must be joking.

Khrushchev and Dwight D. Eisenhower, the American president, might have agreed that China should be invited, but they wouldn’t have agreed which China — the one based in Peking, as it was called then, or Taipei.

Khrushchev’s visit to Pittsburgh on Sept. 24, 1959, came two years before Barack Obama was born. It occurred in a world before manned space travel, when the Princess phone was the ultimate in communication, when the term microwave was something you encountered in a college physics textbook instead of on your kitchen counter.

The centerpiece of the Khrushchev visit was a luncheon speech at the University of Pittsburgh, where he predicted the Soviet Union would overtake the United States and where he asserted that the Soviets’ one party was better than America’s two.

“Come to our country and see how those slaves of Communism live,” he told the 450 people at the Pitt luncheon. “I have come here to see how the slaves of capitalism are living — and I think their living is not a bad one at all.”

Khrushchev’s message in 1959 Pittsburgh was one of conciliation and peace, speaking of “sincere competition in which there will be no bloodshed.” But his remarks, many of them off the cuff, were delivered during what John F. Kennedy two years later would call a “hard and bitter peace,” a peace that later nearly was shattered in Cuba and Berlin and that would spill into bloodshed in Vietnam and Laos.

Fifty years ago Khrushchev told his Pittsburgh audience to “step up your drive — or you will really find yourselves lagging behind us.” Within two years, the Soviets would beat the United States into space, with Yuri Gagarin orbiting the Earth before Alan B. Shepard Jr.’s suborbital flight. But the United States beat the Soviets to the moon — the Soviets never got there — and the American arms buildup of the Reagan years may have contributed to the collapse of the Communist block only 30 years after the visit of Khrushchev, whose name was all but obliterated from Soviet hagiography.

Here in Pittsburgh, Khrushchev listened as Gov. David L. Lawrence described the American political landscape, saying, “To those who do not know us well, we may seem at times a divided people.” Pennsylvania Gov. Edward G. Rendell, who backed Hillary Rodham Clinton over Obama in the 2008 Pennsylvania primary, might give much the same speech today. But he would be giving it in an entirely different context.

Over the past 50 years, the United States has transformed the civil rights movement, in its relative infancy in 1959, from a threat to domestic serenity into an iconic symbol of American democracy. The nation has a black president and has had two black secretaries of state and three female secretaries of state — indeed, there hasn’t been a white male leading the State Department for more than a dozen years. Though the promise of Lenin (a classless society) never was achieved, the promise of Jefferson (a land where all were created equal) may be within reach.

We are accustomed to thinking how perilous is the world in which we live, but it is almost certainly true that the world of Khrushchev’s visit to Pittsburgh was far more dangerous than the one we inhabit now. During his 17 hours here, the Soviet leader warned that the Cold War “could turn into a warm war, or even a hot one — or even a nuclear one that could not only burn, but also incinerate.”

Khrushchev was wrong about many things, but his evaluation of the threat of 1959 was dead right. In the years since then, we have gained a fragile peace but lost our perspective.