On April 12, 1861, the Civil War began.

In 1945, President Franklin D. Roosevelt died at age 63; he was succeeded by Vice President Harry S. Truman.

In 1955, the Salk vaccine against polio was declared safe and effective.

In 1961, Soviet cosmonaut Yuri Gagarin became the first man to fly in space.

In 1963, civil rights leader Martin Luther King Jr. was arrested and jailed in Birmingham, Alabama, charged with contempt of court and parading without a permit. (During his time behind bars, King wrote his “Letter from Birmingham Jail.”)

In 1992, Euro Disneyland (now called Disneyland Paris) opened in MarneLa-Vallee, France.

In 2015, Hillary Clinton jumped back into presidential politics, announcing in a video her second campaign for the White House.