In April 1967, seven years of military dictatorship began in Greece. Thousands of people were arrested and tortured during the rule of the Colonels. Witness speaks to Gerasimos Nortaras, who was part of the armed resistance to the military. He was captured, but refused to give away his fellow fighters, even under brutal torture.

Cuban exiles, backed by the US government, tried to overthrow Fidel Castro in April 1961. But their mission ended in disaster. Witness speaks to Alfredo Duran, one member of the Bay of Pigs invasion force.

Photo: A group of anti-government rebels after their capture by Castro forces (Getty Images)

In the Soviet Union Christians were discouraged from celebrating their main religious festival, Easter. For decades, the atheist state was formally opposed to Christianity, but many believers worshipped in secret. Dina Newman reports.

Photo: Easter procession, Credit: AFP

In April 1989 the Polish trade union Solidarity was legalised once again, after eight years operating underground. It was a key step towards Solidarity’s defeat of the Moscow-backed communist authorities at elections later that year. Witness hears from Solidarity's former spokesman, Janusz Onyszkiewicz.

Photo: Polish Solidarity spokesmen Janusz Onyszkiewicz (L) and Jozef Slisz (R) look on as advisor Bronislaw Geremek calls for the legalisation of independent political parties on 6 June, 1989. (Credit: Getty Images)

An explosion at a train station in North Korea killed around 170 people and destroyed thousands of homes in April 2004. In a rare moment of openness, authorities in Pyongyang asked the United Nations for help. Hear from a Western aid worker who travelled to Ryongchon to assess the damage.

(Photo: North Koreans clear rubble after the Ryongchon train explosion. Credit: Gerald Bourke/World Food Programme/Getty Images)

In post-war Orange County, California, children of Mexican descent were schooled separately from white children until one family took on the system.

Photo: Hoover Elementary School (Mexican only) courtesy of the Mendez family.

American scientists announced they had discovered an effective vaccine against polio in April 1955. It would save millions of children from disability and death. The doctor who led the research was Jonas Salk. Hear from his son Peter and a nurse who worked with him.

Photograph courtesy of March of Dimes: Dr Jonas Salk innoculating his son, Peter.

In April 1979 the brutal Ugandan ruler, Idi Amin, was ousted by invading Tanzanian troops and members of the Ugandan opposition. It was the culmination of a six month conflict between the two countries, which had been triggered by Amin's ill-fated invasion of northern Tanzania.

Idd Lubega, a young sports journalist, recalls those final days.

Photo: Idi Amin with a rocket launcher, April 1979. (Photo by Keystone/Getty Images)

On 9 April, 1989, Soviet troops and tanks crushed a mass demonstration in Georgia's capital Tbilisi. Hear from two demonstrators on the streets of the capital that night.

(Photo: Large crowd of demonstrators in Tbilisi. Credit: Giorgi Tsagareli)

The great American contralto, Maria Anderson, sang outdoors to a vast crowd in Washington DC on 9 April, 1939. She had been barred by one of the city's main concert halls because she was black.

(Photo: Marian Anderson. Hulton Archive/Getty Images)