Although Britain continued to defend the security of Australia and New Zealand as a Commonwealth leader, it was not invited to join the agreement. There were several reasons for this omission. An important concern was that the extension of the invitation to the United Kingdom would have forced the signatories to pave the way for other European powers with colonial interests in the region. Another was the fact that British troops were already in service in Europe and the Middle East, not to mention the commission with the rest of the Commonwealth, making it unlikely that they would actually intervene in the South Pacific in the event of a security crisis. Britain also faced internal instability in its Asian colonies, including Malaya and Hong Kong, prompting the United States to sign an agreement that could force it to intervene to resolve British colonial problems. In any event, the British have already committed to the security of the United States through NATO and Australia and New Zealand through the Commonwealth, so their participation in a Pacific security agreement with the United States, Australia and New Zealand would have been somewhat superfluous. All parties felt that, if the INSTITUANT TREATY WAS finally extended to other powers, the United Kingdom would be among the first to join. Signed on September 1, 1951 in San Francisco, the treaty entered into force on April 29, 1952 and was to remain indefinitely. The Security Treaty of Australia, New Zealand and the United States of America is the non-binding agreement reached in 1951 between Australia and New Zealand, which must cooperate in the military affairs of the Pacific Ocean region. It foresees that an armed attack on one of the three parties would be dangerous to the others and that each of them should act to deal with the common threat.
It has set up a committee of foreign ministers that can meet in consultation. Several developments in Asia between 1949 and 1951 contributed to a change in the American perception of the usefulness of a formal security agreement. The communist victory in the Chinese revolution of 1949 seemed to confirm fears that communism would spread to East Asia and Europe. In the 1950s, the outbreak of the Korean War led Australia and New Zealand to send troops through the UN and NATO allies, expressing both their concern about the threat of communism and their commitment to playing their part in containing it in the region.