Stephen Tuck is a history lecturer at Pembroke College, Oxford, a visiting fellow at the W.E.B. Du Bois Institute at Harvard and the author of “We Ain’t What We Ought to Be: The Black Freedom Struggle From Emancipation to Obama.”

AMERICA remembers the Rev. Dr. Martin Luther King Jr. as a national champion of civil rights. But he was an international icon, too — and like many icons, his legacy was used for a range of purposes that moved far beyond, and even ran counter to, his famous dream.

Indeed, it was King’s “I have a dream” speech that sealed his global fame. We’ve all seen photos of the hundreds of thousands marching in 1963 Washington. But thousands also marched that day in London, Tel Aviv and Accra, Ghana.

In my home country, Britain, support for the march was overwhelming. Many watched King’s speech live via the newly launched Telstar satellite. In London, demonstrators marched to the American Embassy carrying a banner that read, “Your fight is our fight.”

This was more than just an expression of empathy: that summer, Paul Stephenson, a black community organizer in Bristol, led a boycott of the city’s buses. A charismatic and gifted orator, Mr. Stephenson had been to the Deep South to learn tactics and spoke reverently of King’s Montgomery Bus Boycott....