Philip Jenkins, professor of history and religion, Penn State University

For several years leading up to June 22, 1941, it had looked as though dictators and militarists would soon rule virtually the whole world outside North America. But Operation Barbarossa—Germany’s decision to send 3 million of its soldiers smashing across the Soviet border—would ultimately lead to Hitler’s defeat and the destruction of Nazism.

Neera Tanden, president, Center for American Progress

By empowering half the population with the responsibilities of citizenship, August 26, 1920—the day women gained the right to vote—allowed the U.S. to live up to its fundamental values of opportunity and equality.

Paul Kennedy, professor of history, Yale University

The day Thomas Newcomen invented his steam engine. America would be like a giant Angola without it.

Freeman Dyson, professor emeritus of physics, Institute for Advanced Study

The day the asteroid hit the Yucatán Peninsula and wiped out the dinosaurs, making room for our little primate ancestors to grow big and brainy and to take over the planet.

Note: This article originally stated that Freeman Dyson is a professor emeritus at Princeton University.

Diana Gabaldon, author of the Outlander series

The day, in 1675, that Anton van Leeuwenhoek first looked through the lens of the microscope he invented. There are a whole lot of people making history who wouldn’t have been here save for the discoveries that followed from that drop of pond water.

W. Kamau Bell, host, Totally Biased With W. Kamau Bell

There’s no way I can get this correct, so: It has to have affected me personally. It has to have had a big impact on America, culturally and historically. And it has to have involved sequins. Therefore, the obvious answer is May 16, 1983, when Michael Jackson first performed the moonwalk on TV. I think it’s one of the reasons we have a black president today. People went, Wow, black people are sort of magical. And Barack Obama is basically a walking sequin.

Oliver Stone, director and co-author of The Untold History of the United States

July 20, 1944, when Henry Wallace lost the vice-presidential nomination at the Democratic Convention in Chicago. Had he won, Wallace, not Harry S. Truman, would have become president when Roosevelt died. The U.S. would have had a much better relationship with the Soviet Union, and I don’t think Wallace would have dropped the atomic bomb on Japan.

Anne-Marie Slaughter, Atlantic contributing editor and professor of politics and international affairs at Princeton University

Trite as it may seem, the signing of the Declaration of Independence on July 4, 1776, was the first public assertion of human equality as a legitimate rationale for political action. The Declaration would eventually eat away at the formal barriers of gender, race, religion, ethnicity, sexual orientation, and any other differences that human beings have created to hold some down and raise others up.

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