On March 4, 1968, civil rights leader Martin Luther King Jr. was killed.

The U.S. has several unforgettable moments that caused course changes for us as a country and made each of us take a moment and reflect on life.

For those alive during each of these events, most will remember exactly where they were when they heard about the event.

Martin Luther King Jr. assassination

Though the Civil Rights Act of 1964 alleviated many of the rights violations against African-Americans, in the eyes of King the fight was not yet done, and he spent his remaining four years speaking out on various subjects. Eventually the celebrated civil rights leader was gunned down on his motel room balcony.

Fall of the Berlin Wall
Sue Ream

For the latter half of the 20th century, nuclear war loomed as the Cold War stayed in place from the end of World War II to the collapse of the Soviet Union. But to many, one of the biggest signs of the end of the Cold War was the collapse of the Berlin Wall, a physical boundary between the East and the West.

The Imperial Japanese attack on Pearl Harbor
Associated Press

"Dec. 7, 1941, a date which will live in infamy." -- President Franklin Roosevelt.

On this day, forces of the Imperial Japanese navy attacked the home base of the U.S. Pacific fleet before a formal declaration of war was issued. The attack saw nearly 3,500 U.S. casualties along with a majority of the Pacific fleet and aircraft destroyed or damaged, and marked America's entry into World War II.

V-E and V-J Day

A sailor kissing a random woman in the streets of New York City. That about sums up the crazed sensation in the U.S. after Germany was defeated in Europe —Victory in Europe day, also known as V-E Day, celebrated on May 8, 1945.

Similarly, Japan surrendered in the Pacific on Aug. 15, 1945 (Victory over Japan day, also known as V-J Day) — which was announced in the U.S. on Aug. 14, 1945, due to time zone differences.

These days marked the end of the bloodiest conflict in world history and the start of America's new life as a world super power.

The Trinity test
Associated Press

Though not disclosed to the public, the July 16, 1945, date marking the first-ever nuclear weapon test green-lighted the dropping of two nuclear bombs on Japan. It also marked the dawn of an age in which humanity could be wiped out in a war between two nuclear-armed powers.

Sputnik and the start of the space race
Associated Press

On Oct. 4, 1957, the Soviet Union launched Sputnik 1, the world's first artificial satellite, signaling the launch of the space race. The fact that the Soviets were the first to launch a satellite came as a shock to millions of Americans, who watched the little blip of light fly through the night sky.

March on Washington for jobs and freedom
Associated Press

The 1960s was the defining decade for civil rights, culminating with the march on Washington for jobs and freedom in which 200,000-300,000 civil rights supporters descended on the U.S. Capitol. The most memorable moment of the march was Martin Luther King Jr.'s "I Have a Dream" speech.

JFK assassination

John F. Kennedy's assassination in Dallas on Nov. 22, 1963, shook the nation and marked a grim time for Americans' faith and trust in government as the turbulent 1960s got under way.

Man walks on the moon
Associated Press

JFK predicted that U.S. astronauts would be on the moon in the 1960s, and America landed the first man on the moon on July 20, 1969.

Millions of Americans tuned in to watch footage of Neil Armstrong take the first step on the lunar landscape.

Nixon resigns amid Watergate scandal
Associated Press

As if the assassination of JFK and the unpopular war in Vietnam weren't enough, American confidence in government was further shaken when the once popular Richard Nixon resigned rather than be impeached for his role in the Watergate scandal. Nearly every government scandal involving presidents after this has had the word "gate" put on the end.

The Iranian hostage crisis
Associated Press

The Iranian hostage crisis had a profound impact on America and essentially ended a president's hopes of re-election. It set the stage for three decades of hostility between the U.S. and Iran after an Iranian mob stormed the American Embassy in Tehran. For 444 days, 52 hostages were held by the Iranians, and a rescue attempt resulted in eight American deaths. The event received widespread coverage in the U.S. and was marked by a surge of patriotism.

The Challenger disaster

On an unusually chilly morning on Jan. 28, 1986, the space shuttle Challenger experienced a faulty O-ring mid-launch, leading to destruction of the shuttle, and the death of the seven astronauts on board.

Caught on film, the tragedy shocked the nation. President Ronald Reagan canceled the State of the Union address that night in order to address the tragedy instead.

Nineteen years later, the space shuttle Columbia would implode during re-entry, causing a similar shock to the nation.

Sept. 11, 2001

After the Cold War ended, America generally seemed at peace. But on that September morning, terrorists crashed jets into the World Trade Center towers in New York City, the Pentagon and a field in Pennsylvania. About 3,000 Americans were killed in the attacks and many more injured in a morning that shocked and haunted the nation.