Newly-declassified documents released by Britain's Public Record Office on Thursday contained some fascinating revelations. According to a letter dated March 19, 1969, Britain and the United States were seriously discussing plans for a military conflict with the Soviet Union, in the wake of the Warsaw Pact invasion of Czechoslovakia. And as reports, London and Washington believed the NATO alliance could have collapsed if Soviet influence had been allowed to extend further into Europe. His report begins with a Czechoslovak Radio announcement from