Following World War I, the League of Nations granted Australia mandate to administer the former German colony. 
Both Papua and New Guinea remained under separate administrations until the World War II when the Japanese invaded and took control of all of coastal New Guinea and the Oro and Milne Bay districts of Papua. Their attempts to take Port Moresby from the sea were frustrated by the Battle of the Coral Sea, and over land they were beaten back by the Australians on the Kokoda Track. The war had a huge impact on all of those areas affected by it.
The myth of the all powerful white man was destroyed. Local people who worked with the Americans were astounded to see black soldiers apparently on par with their white comrades, and even the Australian soldiers were friendly in ways unlike their pre war ‘mastas’. Local people also were astonished by the amount of cargo that arrived with the armed forces.
The largest navel base in the South-west Pacific was established on Manus, with nearly 1 million Americans passing through as they prepared to attack the Philippines. At the end of the war some 150,000 Japanese soldiers lay dead in the PNG soil. In New Ireland Japanese garrisons were stationed at Kavieng and Namatanai and missionaries and plantation owners were caught up in the final stages as described in the Battle for Kavieng when the Japanese executed the interned prisoners comprising priests and plantation owners. The German and Italian missionaries from Namatanai and Lihir were caught up in this action.
Lihirians were involved in the Second World War as labourers, carriers and messengers for both the Allied and the Japanese troops. Many elderly Lihirians recall the high number of Lihirians absent during this time and the particularly harsh experiences underneath the Japanese.