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. It was the first arms control agreement established during the Cold War, setting aside the continent as a scientific preserve, establishing freedom of scientific investigation, and banning military activity; for the purposes of the treaty system, Antarctica is defined as all the land and ice shelves south of 60°S latitude. Since September 2004, the Antarctic Treaty Secretariat, which implements the treaty system, is headquartered in Buenos Aires, Argentina. The main treaty was opened for signature on December 1, 1959, and officially entered into force on June 23, 1961. The original signatories were the 12 countries active in Antarctica during the International Geophysical Year (IGY) of 1957–58: Argentina, Australia, Belgium, Chile, France, Japan, New Zealand, Norway, South Africa, the Soviet Union, the United Kingdom, and the United States. These countries had established over 55 Antarctic research stations for the IGY, and the subsequent promulgation of the treaty was seen as a diplomatic expression of the operational and scientific cooperation that had been achieved. , the treaty has 56 parties. History 1940s After the Second World War, the U.S. considered establishing a claim in Antarctica. From August 26, 1946, and until the beginning of 1947, it carried out Operation Highjump, the largest military expeditionary force that the United States had ever sent to Antarctica, consisting of 13 ships, 4,700 men, and numerous aerial devices. Its goals were to train military personnel and to test materiel in conditions of extreme cold for a hypothetical war in the Antarctic. On September 2, 1947, the quadrant of Antarctica in which the United States was interested (between 24° W and 90° W) was included as part of the security zone of the Inter-American Treaty of Reciprocal Assistance, committing its members to defend it in case of external aggression. In August 1948, the United States proposed that Antarctica be under the guardianship of the United Nations, as a trust territory administered by Argentina, Australia, Chile, France, the United States, the United Kingdom, and New Zealand. This idea was rejected by Argentina, Australia, Chile, France, and Norway. Before the rejection, on August 28, 1948, the United States proposed to the claimant countries some form of internationalization of Antarctica, and this was supported by the United Kingdom. Chile responded by