The Antarctic Treaty and related agreements, collectively known as the Antarctic Treaty System (ATS), regulate international relations with respect to Antarctica, Earth's only continent without a native human population. For the purposes of the treaty system, Antarctica is defined as all of the land and ice shelves south of 60°S latitude. The treaty entered into force in 1961 and currently has 54 parties. The treaty sets aside Antarctica as a scientific preserve, establishes freedom of scientific investigation, and bans military activity on the continent. The treaty was the first arms control agreement established during the Cold War. Since September 2004, the Antarctic Treaty Secretariat headquarters has been located in Buenos Aires, Argentina. The main treaty was opened for signature on December 1, 1959, and officially entered into force on June 23, 1961.