Johnson was concerned with averting the possibility of nuclear war, and he sought to reduce tensions in Europe. The Johnson administration pursued arms control agreements with the Soviet Union, signing the Outer Space Treaty and the Treaty on the Non-Proliferation of Nuclear Weapons, and laid the foundation for the Strategic Arms Limitation Talks. President Johnson held a largely amicable meeting with Soviet Premier Alexei Kosygin at the Glassboro Summit Conference in 1967; then, in July 1968 the United States, Britain, and the Soviet Union signed the Non-Proliferation Treaty, in which each signatory agreed not to help other countries develop or acquire nuclear weapons. A planned nuclear disarmament summit between the United States and the Soviet Union was scuttled after Soviet forces violently suppressed the Prague Spring, an attempted democratization of Czechoslovakia.