Max Pearson presents a collection of this week’s Witness History episodes from the BBC World Service.It's 75 years since the founding of Nato. In 1949, a group of 12 countries formed the North Atlantic Treaty Organization to block the expansion of the Soviet Union.Professor Sten Rynning, the author of "Nato: from Cold War to Ukraine", talks about some of the most significant moments in Nato's history.It's 30 years since the beginning of the Rwandan genocide. We hear from one of the survivors. This programme contains disturbing content.Plus Britain's Mirpuri migration, the origins of the Heimlich Manoeuvre and Britain's first nudist beach.Contributors: Sten Rynning - Professor of War Studies at the University of Copenhagen Riyaz Begum - migrated from Mirpur to London Antoinette Mutabazi - Rwandan genocide survivor Janet Heimlich - daughter of Dr Henry Heimlich Adam Trimingham - Brighton based journalist David Johnson - nudist (Photo: British Foreign Secretary Ernest Bevin signs the North Atlantic Treaty. Credit: Keystone/Hulton Archive/Getty Images)