The Antarctic Treaty and related agreements, collectively called the Antarctic Treaty System or ATS, regulate international relations with respect to Antarctica, Earth's only continent without a native population. For the purposes of the treaty system, Antarctica is defined as all land and ice shelves south of the southern 60th parallel. The treaty has now been signed by 46 countries, including the Soviet Union (now defunct) and the United States, and set aside Antarctica as a scientific preserve, established freedom of scientific investigation and banned military activity on that continent. This was the first arms control agreement established during the Cold War.