As members of the British Empire, Australia and New Zealand were obligated to enter World War II when Britain joined in on September 3, 1939. As a result of this, these two geographically isolated states were vulnerable to attacks from the Axis powers throughout the war. Australia, for example, suffered suffered a series of air raids in the city of Darwin between 1942 and 1943 as a result of Japanese forces that managed to expand further south of the Pacific ocean.
Following the war the focus of the Allied powers were directed towards the reconstruction of Europe and Japan. Australia and New Zealand, however, were worried about the possibility of expansionism from Japan and the rise of communism. This led to an agreement between the two states, which states that the two countries will work together with regards to international affairs as they share common goals and security concerns. The agreement was signed prior to the end of World War II and was the first agreement both states negotiated independently and was a sign for Britain that Australia and New Zealand felt left out of their post-World War II planning efforts. This allegation was confirmed through the signing of the North Atlantic Treaty in 1949.
In April 1951 President Harry Truman announced negotiations between the United States and Australia and New Zealand regarding a security agreement, which also occurred during the final peace treaty with Japan. On September 1, 1951 the Australian, New Zealand, and United States (ANZUS) Treaty was signed in San Francisco, California and was taken into full effect on April 29, 1952. The general purpose of the treaty was to protect the security interest of each country and the Pacific Rim. The purpose of the ANZUS Treaty expanded in 1954 through the overarching Southeast Asian Treaty Organization (SEATO), which included Britain, France, ANZUS, and other Asia states.
The agreement for the ANZUS Treaty started to meet some trouble when New Zealand became a nuclear-free zone and eventually refused to allow U.S. nuclear-powered submarines to dock in any of its ports. As a result, U.S. Secretary of State George P. Shultz and Australian Foreign Minister Bill Hayden confirmed that the two states will uphold their agreements with each other, which is outlined in the ANZUS Treaty. Despite these reports, the United States ended its treaty obligations towards New Zealand on September 17, 1986. With the United States ending its ANZUS Treaty obligations, the United States and New Zealand no longer maintain security relationships – this “agreement” has not been formally verified by both states till this day.