Which international agreement established the modern legal framework for Antarctica?

The Antarctic Treaty established the modern legal framework for Antarctica.

The treaty was signed in Washington, D.C., on 1 December 1959 by 12 countries that had been active during the International Geophysical Year. It entered into force on 23 June 1961 and applies to the area south of 60 degrees south latitude.

The agreement reserves Antarctica for peaceful purposes and prohibits military measures such as weapons testing and military manoeuvres. It also guarantees freedom of scientific investigation and requires that scientific results be shared. The treaty placed territorial sovereignty claims into a holding pattern rather than resolving them.

The wider Antarctic Treaty System later gained environmental agreements and rules governing conservation, waste, and marine resources. The 1991 Environmental Protocol designated Antarctica a natural reserve devoted to peace and science and prohibited mineral-resource activities except scientific research. The treaty does not make Antarctica a country or give it a single national government.