Spiro Agnew for vice president. August 11 – The last steam passenger train service runs in Britain. A selection of British Railways steam locomotives make the 120-mile journey from Liverpool to Carlisle and return to Liverpool – the journey is known as the Fifteen Guinea Special. August 18 – Two charter buses are forced into the Hida River on National Highway Route 41 in Japan in an accident caused by heavy rain; 104 are killed. August 20–21 – Warsaw Pact invasion of Czechoslovakia: The 'Prague Spring' of political liberalization ends, as 750,000 Warsaw Pact troops and 6,500 tanks with 800 aircraft invade Czechoslovakia, the largest military operation in Europe since the end of World War II. August 24 – Canopus (nuclear test): France explodes its first hydrogen bomb in a test at Fangataufa atoll in French Polynesia. August 22–30 – Police clash with anti-war protesters in Chicago outside the 1968 Democratic National Convention, which nominates Hubert Humphrey for U.S. president and Edmund Muskie for vice president. The riots and subsequent trials are an essential part of the activism of the Youth International Party. August 29 – Crown Prince Harald of Norway marries Sonja Haraldsen, the commoner he has dated for 9 years. September–October September 6 – Swaziland (now eSwatini) becomes independent. September 7 The crash of Air France Flight 1611 kills 95 people, including French Army General René Cogny, as the Caravelle jetliner plunges into the Mediterranean Sea while making its approach to Nice following its departure from the island of Corsica. The International Association of Classification Societies (IACS) is founded. September 13 Albania officially withdraws from the Warsaw Pact upon the Soviet Union-led Warsaw Pact invasion of Czechoslovakia, having already ceased to participate actively in Pact activity since 1962. September 17 – The D'Oliveira affair: The Marylebone Cricket Club tour of South Africa is cancelled when the South Africans refuse to accept the presence of Basil D'Oliveira, a Cape Coloured, in the side. September 21 – The Soviet's Zond 5 uncrewed lunar flyby mission returns to earth, with its first-of-a-kind biological payload intact. September 23 – Vietnam War: The Tet Offensive comes to an end in South Vietnam. September 27 – Marcelo Caetano becomes prime minister of Portugal. September 29 – A referendum in Greece gives more power to the military junta. October 2 – Tlatelolco massacre: A student demonstration ends in bloodbath at La Plaza de las Tres