security treaty between Australia, New Zealand, and the United States that was signed in San Francisco, Calif., on Sept. 1, 1951, for the purpose of providing mutual aid in the event of aggression and for settling disputes by peaceful means. It came into force in 1952. The three countries' initials provided the acronyms for the treaty and the organization that grew out of it. The United States offered the pact to Australia as compensation for the prospect of Japanese rearmament. Under the terms of the treaty, the three nations maintained a consultative relationship with each other and strove to ensure their collective security in the Pacific region.

In the mid-1980s New Zealand instituted an antinuclear policy, one of whose provisions was the banning of nuclear-armed vessels from its ports, including those of the U.S. Navy. In response, the United States formally suspended its treaty obligations to New Zealand in 1986 and reduced the two countries' military ties. The three nations remained formal parties to the treaty, but in practical terms ANZUS was inoperative from then on.