On this date in history:
In 1859, Frenchman Jean Francois Gravelet, known professionally as the Great Blondin, became the first daredevil to walk across Niagara Falls on a tightrope.
In 1870, Ada Kepley became the first woman to graduate from an accredited law school in the United States -- Union College of Law in Chicago.
In 1905, the theory of relativity was introduced by Albert Einstein in "On the Electrodynamics of Moving Bodies."
In 1908, a spectacular explosion occurred over central Siberia, probably caused by a meteorite. The fireball could be seen hundreds of miles away.
In 1934, German leader Adolf Hitler ordered a bloody purge of his own political party -- the so-called Night of the Long Knives. Hundreds of Nazis he feared might become political enemies were assassinated.
In 1950, U.S. troops were moved from Japan to help defend South Korea against invading North Koreans.
In 1971, three Soviet Cosmonauts, members of the crew of the world's first space station, were killed when their spacecraft depressurized during re-entry.
In 1982, the extended deadline for ratification of the Equal Rights Amendment expired, three states short of the 38 needed for passage.
In 1988, the Roman Catholic Church excommunicated French Archbishop Marcel Lefebvre after he consecrated four bishops in defiance of Pope John Paul II.
In 2009, Yemenia Airways Flight IY626, which had taken off from Sanaa, Yemen, crashed into the Indian Ocean while trying to land at Moroni, the capital of Comoros, killing 152 of 153 people aboard. The lone survivor was 14-year-old Bahia Bakari, who became known as "the miracle girl."
In 2013, the Yarnell Hill wildfire in Arizona killed 19 firefighters on what Gov. Jan Brewer called "as dark a day as I can remember." On July 9 in Prescott, thousands of people, including firefighters from across the country, attended a memorial service for the victims, all members of specialized firefighting unit called the Granite Mountain Hotshots.
In 2014, the U.S. Supreme Court ruled that family-owned corporations can't be required to pay for insurance coverage for contraception under the Affordable Care Act.
In 2015, the American Ballet Theater promoted Misty Copeland to be principal dancer -- the highest rank within a professional dance company. She was the first African-American woman to hold the post for the company.
In 2017, the German parliament passed legislation legalizing same-sex marriage after Chancellor Angela Merkel, who voted against the measure, encouraged her party to vote their conscience.
In 2019, Donald Trump made history by becoming the first sitting U.S. president to step foot on North Korean soil during a meeting with leader Kim Jong Un.