Australia joined with the United Kingdom in declaring war on September 3, 1939 on Germany. New Zealand did so also, preferring to send a separate letter to demonstrate independence. New Zealand and Australian units served in North Africa, Italy, and Greece and rendered good service. When the Japanese attacked around Asia and the Pacific in December 1941, the overseas units were rushed home as part of the agreement Australia and New Zealand signed with England at the start of the war. Some were sent to Singapore, where they were surrendered on February 17, 1942. Two days later, the Japanese bombed Darwin, sinking 26 ships.
England could no longer guarantee their support due to the war in Europe. In December 1941, the Australian government publicly asked for American assistance. That assistance would come with a price that Australia could not imagine in 1941.
In March 1942 MacArthur, fresh from his retreat in the Philippines, took stock of his new command, Supreme Commander Southwest Pacific. He found that he had few of his countrymen to command. Until early 1944, the Australians would make up the bulk of his forces. The friction between MacArthur and his Australian subordinates would compromise the Allied operations in New Guinea.
Australia and New Zealand provided the Allies, especially Britain, with many needed supplies. New Zealand rationed its own food supply to increase the amount that could be sent to England.