Portrait of President George Washington.

Portrait of President Thomas Jefferson.

Photo of Abraham Lincoln, 16th president of the United States.

Photo of Theodore Roosevelt.

Photo of President Woodrow Wilson.

Photo of President Franklin Delano Roosevelt.

President John F. Kennedy.

Photo of President Ronald Reagan.

Photo of President Bill Clinton.

Photo of President George W. Bush.

Official photo of Barack Obama, the current president.

Famous scientist Albert Einstein. After Nazis took over in the 1930s, he emigrated to the United States.

Scientist Dr. Jonas Salk (left), receives a gold medal from President Eisenhower for curing polio.

Confederate General Robert E. Lee surrenders to Union General Ulysses S. Grant at Appomattox Courthouse.

Portrait of Eli Whitney, inventor of the Cotton Gin and interchangeable parts.

Thomas Edison, inventor of the light bulb, among other things.

Senator Joe McCarthy, rabidly anti-communist politician of the 1950s.

Famous American writer Mark Twain.

Painting of the signing of the Declaration of Independence by John Trumbull.

Painting of the Battle of Bunker Hill also by John Trumbull.

Surrender of General Burgoyne painting by John Trumbull.

Surrender of Lord Cornwallis by John Trumbull.

General George Washington resigning his commission by John Trumbull.

 Portrait of Alexander Hamilton, Secretary of the Treasury. 

Elizabeth Eckford, one of the Little Rock Nine, being escorted by National Guard into Little Rock Central High School in 1957.

Martin Luther King Jr. delivering his famous "I Have a Dream" speech in 1963.

The turnout at Washington Monument for the "I Have a Dream" speech.

President Abraham Lincoln delivering his Gettysburg Address. Picture from americanrectoric.com.

Martin Luther King Jr. on the Lorraine Motel balcony just before he was shot and killed. Image from nydailynews.com.

Sketch of the Great Chicago Fire of 1871.

World Trade Center burning after the planes crashed.

American soldiers raising the flag at Iwo Jima during World War II.

The first flag raising at Iwo Jima.

The USS Arizona sinking after the attack at Pearl Harbor on December 7, 1941.

Dust storm goes through Manzanar Japanese-American internment camp during World War II.

Japanese representatives aboard the USS Missouri, about to sign the Japanese Instrument of Surrender on September 2, 1945.

Sketch of the Alamo in 1854.

President George W. Bush having Thanksgiving dinner in Baghdad in 2003.

President Obama signing healthcare reform in 2010. Image from nytimes.com.