How did the allies stop the japanese from overrunning australia

Despite Australian fears, the Japanese never intended to invade the Australian mainland. While an invasion was considered by the Japanese Imperial General Headquarters in February 1942, it was judged to be beyond the Japanese military's capabilities and no planning or other preparations were undertaken. Instead, in March 1942 the Japanese military adopted a strategy of isolating Australia from the United States by capturing Port Moresby in New Guinea and the Solomon Islands, Fiji, Samoa and New Caledonia. This plan was frustrated by the Japanese defeat in the Battle of the Coral Sea and was postponed indefinitely after the Battle of Midway.

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