Common English ancestry and cultural heritage -- plus a similar "frontier" experience -- have made the United States and Australia natural allies. Still, the U.S. and Australian relationship is very much born of war. Their shared efforts as allies in both World Wars I and II, the Cold War and War on Terror have strengthened that alliance.
The Crucible Of World War II
World War II was central in cementing the U.S.-Australian relationship. The two signed a treaty of bilateral diplomatic relations in January 1940, nearly two years before Japan attacked U.S. bases in Hawaii and the Philippines in December 1941.
Japan's plan for the South Pacific was to drive the United States out of the Philippines, clearing the way for Japanese occupation of the Dutch East Indies, which were rich in oil. The Japanese attack on Pearl Harbor was designed to knock the American navy out of the Pacific long enough for Japan to establish a defensive perimeter just south of the Dutch Indies. As such, Japan had no concrete plans for invading Australia.
However, Japan did not want the United States using bases in northern Australia to launch air attacks on their defenses. Thus, Japan targeted the Australian cities of Darwin (which the Japanese hit with more bombs than they dropped on Pearl Harbor) and Broome. Japan designed other attacks in an attempt to draw American attention away from imperial naval maneuvers in the Coral Sea, just northeast of Australia, and Midway Island near Hawaii. The diversions did not work, and the U.S. Navy beat the Japanese Navy in both the Coral Sea and at Midway, effectively reversing the offensive and defensive roles of the belligerents in the Pacific.
As Japan forced the American evacuation of the Philippines in May 1942, U.S. General Douglas MacArthur sped south to Australia. From there he planned the slogging U.S. offensive through the Solomon Islands and New Guinea that would lead American forces back to the Philippines.
According to the U.S. State Department, after World War II, Australia worked with the United States and other founding members to form the United Nations. The United States established similar mutual defense treaties around the globe to help contain the spread of Communism and protect allies from Communist attack. Along with New Zealand, the U.S. and Australia formed the ANZUS Treaty of 1951. ANZUS was essentially the NATO of the South Pacific. It pledged the member nations to mutual aid if any of the other members were attacked.
In 1984, New Zealand stopped allowing American nuclear-capable or nuclear-powered ships to dock in her ports. The U.S. suspended its obligations to New Zealand under ANZUS. Nevertheless, the U.S. and Australia retain the bi-lateral function of the ANZUS agreement.
War On Terror
After Al-Qaeda terrorists attacked the World Trade Center and the Pentagon on September 11, 2001, the United States and Australia jointly enacted the mutual defense aspect of the ANZUS treaty. Australia committed troops to both the American invasions of Afghanistan and Iraq.
The State Department reports that Australian forces largely use American-designed military equipment, including the M1A1 Abrams tank, and F-111, F/A-18, and C-17 airlift aircraft. The U.S.-Australia Defense Cooperation Treaty of 2007 facilitated continued trade of military technology.
Obama Renews Focus On The Pacific
On November 16, 2011, U.S. President Barack Obama announced that the United States is stationing 250 Marines at an Australian military base in Darwin. While the U.S. and Australia have consistently conducted training exercises since the inception of ANZUS in 1951, U.S. troops have not been permanently stationed in Australia in some time. Obama said that current plans call for 2,500 troops to rotate through Darwin. Obama announced the plan at a joint conference in Canberra, Australia, with Australian Prime Minister Julia Gillard.
According to the Washington Post, the announcement indicates a foreign policy change for Obama's administration. As he is ending American involvement in Iraq and drawing down troop strength in Afghanistan, the Australian move puts a token American force south of burgeoning China to keep watch on security on the South Pacific.
China appeared angered by Obama's announcement. Nevertheless, Obama indicated that American presence in the area will ensure that China operates by a "clear set of principles" as it grows economically and politically.