Background

The Australian government and people feared an attack from Japan after the fall of Singapore because they were in no condition to fight, as the Royal Australian Air Force was not up to date with modern aircraft and the small size of the Royal Australian Navy could not compete with the Imperial Japanese Navy. The Australian Army was also not much stronger as it had inexperienced units, but to solve this issue the Australian Government expanded their military units from all sides by gathering troops from other assignments to transfer into the pacific.

The Japanese had a goal to capture Port Moresby in Papua New Guinea to stop trade connections from the United States to Australia. This port was a target because it would allow the Japanese to reach Australia's most populated and industrial areas along the coast, including Melbourne, Sydney and Brisbane. It would also give them control over the trade that Australia has with other nations like the USA because the route through the Pacific and Indian Ocean would be covered by the Japanese troops.

It was believed that the Japanese originally wanted to invade Australia but thought it was too much of a risk and beyond their capability, so instead they played the safer option and decided to capture Port Moresby and the surrounding islands to isolate Australia from the bigger powers. After an attempt at Port Moresby through the waters, they resolved to trekking along the Kokoda track to attack from the Owen Stanley Ranges instead, while Australia allied with the USA for naval force.