The civil rights movement got that support from the elites when the Democratic Party backed a civil rights bill during its convention in 1948, even though Southern white Democrats walked out, Kazin says.
Five years later, another group of elites lent their support to the movement. The U.S. Supreme Court ruled that the separate but equal doctrine was unconstitutional in Brown vs. Board of Education.
"The Supreme Court unanimously said that segregation was wrong," Kazin says. "They had an impact."
A movement, though, can't appeal to the altruism of elites to get their support. Elites help movements when they feel their own interests are threatened, says Pizzigati, author of "The Rich Don't Always Win."
That cold calculus among the rich is what made the New Deal possible, he says.
Economic conditions were so bad in America during the 1930s that many of the rich in America feared social upheaval, he says. The rich were being blamed for miserable economic conditions. People feared revolution. In 1932, the Communist Party held a rally in New York -- 60,000 people showed up as nervous police officers with machine guns looked on, Pizzigati says.
The people at the top feared that social instability would cause American society to crumble. They were people like Randolph Paul, a wealthy Wall Street tax lawyer who warned other wealthy Americans that they were courting disaster, Pizzigati says.
"Paul became such a fierce advocate for very high taxes on the American rich because he said that we could not tolerate the level of income inequality in the U.S., that it was going to bring the country down," Pizzigati says.
Other wealthy Americans bought into Paul's rationale. They allowed their taxes to go up. The Cold War helped as well. Communists said capitalism spawned yawning gaps between the rich and poor, and the American elite wanted to prove them wrong, Pizzigati says.
And they were willing to pay the price to make these changes possible, he says. By 1961, a married couple's income over $400,000 was taxed at a 91% rate, Pizzigati says.
The rich weren't as rich, but America's middle class was booming, Pizzigati says.
"We had a fundamental economic shift," Pizzigati says. "The plutocracy that had existed at the beginning of the 20th century had essentially disappeared. We went from a place that was two-thirds poor to two-thirds middle-class."
Could people without power spark such a movement today?
Palmer, author of "Healing the Heart of Democracy," believes they can. He is the founder of the Center for Courage & Renewal, a nonprofit that often works with activists through programs and retreats.
He says younger activists are more adept at coalition building.
"The young people today walk across lines of difference like they're not even there," he says. "My generation didn't walk across lines of sexual orientation, race or religion as easily as these kids. For a lot of them, it's not even noticed."
Still, there is one final lesson for anyone who wants to join a movement. Victory is fleeting and setbacks are inevitable. At times, it can seem like it was all a waste.
King fought such a letdown later in his life.
Five years after he delivered his "I Have a Dream" speech, he gave a different one at a church in Memphis, Tennessee. The crowds weren't hanging onto his words like they once did. He had become unpopular because of his opposition to the war in Vietnam. Black militants scorned his nonviolent approach. And his plan to create a multiracial army of poor people to occupy Washington was floundering.
Yet he told the shouting audience at the Memphis church that "we as a people will get to the Promised Land."
King was assassinated the next day as he stood on the balcony of a motel chatting with his friends below.
He would not live to see his birthday turned into a national holiday. He wouldn't see the first black president elected. And he wouldn't see his four children become adults.
Those who give the most to a movement often don't see the rewards of their risk.
"We plant the seeds, but we don't know what the crop will look like," Palmer says.
That is perhaps the harshest lesson of all.