Once upon a time, America practiced international diplomacy with a cornet, a piano, and a trumpet.

The results, fascinatingly chronicled in The Jazz Ambassadors Friday at 10 p.m. ET on PBS (check local listings), were stranger and more revealing than anyone could have imagined.

The idea seemed simple enough. The U.S. Information Agency (USIA), formed in the 1950s to promote the American Cold War brand abroad, would send American jazz musicians to places like Africa, India, and even the Soviet Union.

New York Congressman Adam Clayton Powell had persuaded the USIA that jazz concerts would show off an American product so indisputably endearing that everyone who heard it would be more likely to love us.  

Now you might think conducting Cold Warfare with Dizzy Gillespie’s trumpet and Duke Ellington’s keyboard, rather than with strutting threats of “what we can do to you,” was inherently a good idea.

Musically, it was. Tens of thousands of people showed up to see Diz, Duke, Benny Goodman, Louis Armstrong (top) and others set auditoriums on fire.

But there were problems, and The Jazz Ambassadors lays them out in often somber detail.

One of the government’s primary motivations for sending these musicians to those countries, many of which were still under colonial rule, is that America had a big Cold War PR problem.

It was clear that many of those “Third World” nations would soon be free agents, which meant they would be picking a side between The West, led by America, and the communist bloc, led by the Soviet Union.

America’s recruitment pitch relied heavily on “freedom,” the notion that in America, all people could exercise beautiful inalienable rights. 

The problem: It wasn’t exactly a secret that when America said “all people,” it meant white people. Black and brown people had been systematically excluded for virtually all of American history.

The Soviets were not shy about reminding the world of this. A Soviet propaganda cartoon, shown in The Jazz Ambassadors, has a car driving down a highway flanked by electrical wires from which an endless stream of black bodies dangle with nooses around their necks.

“Strange Fruit,” anyone?

Now Southern and other conservative legislators never liked the idea of the jazz tours in the first place, largely because that’s not who they wanted to see representing America.

The reason President Dwight Eisenhower went along with it anyway, The Jazz Ambassadors suggests, is that the USIA sold it as an antidote to America’s tarnished racial image.

Look, here are all these black American musicians, playing this wonderful music. How bad could things be?

Artists like Gillespie were torn. On the one hand, they loved the idea of playing their music for the world.  

On the other hand, they didn’t want to be used as a sleight-of-hand promotional trick to make it look like America really practiced that “all men are created equal” business.

When Gillespie was told he would be briefed on how to respond to questions overseas, he declined.

“I’ve got 300 years of briefing,” he said. “I know what they done to us.”

Armstrong, not normally considered militant, had an even stronger reaction.

He had been talking with the USIA through the summer of 1957 about doing one of their tours and was close to an agreement when Arkansas Gov. Orval Faubus tried to stop six black children from enrolling in Little Rock public schools that September.

Eisenhower refused to send federal troops to ensure the safety of the students, after which Armstrong called the president “two-faced” and cut off negotiations. He also called Faubus a 12-letter word that didn’t make it into any publication.

“They’ve been ignoring the Constitution,” Armstrong said.

 Several years later Armstrong did agree to a tour of Africa, where those emerging nations hailed him.

The tours continued for about ten years, during which time some Americans back home did not help with the image-burnishing mission. Birmingham Sheriff Bull Connor’s 1963 attacks on civil rights demonstrators with police dogs and fire hoses provided visual images it was hard to erase with even a Duke Ellington or Dave Brubeck number.

As cultural diplomacy, however, The Jazz Ambassadors suggests the USIA program succeeded on all levels, including several that weren’t in the prospectus.  

The tours showed, says narrator Leslie Odom Jr., that America could and would listen to the world, even when it was telling us that some things in America were not working.

It didn’t mean we fixed those things right away. It did mean we were talking or at least thinking about them, instead of simply declaring we’re right and the rest of you need to deal with it.

In that sense, ironically, the segregationists were right. Music spoke a language they didn’t want to hear.