From August 1945 it was possible to begin to calculate the cost of the war on Bougainville. The American Marines had lost 436 dead. With other losses in the American Army and those of aircrew the total American dead was probably close to 1,000. The 42 Fijians who died in the Solomons included those who were killed accidentally, those who had died of illness and one, Corporal Sikanaivalu, who died winning a Victoria Cross. Most of the New Zealanders who died in the Pacific were in the air force, and while they rarely died in Bougainville many had taken-off from fields at Torokina and Nissan: Royal New Zealand Air Force (RNZAF) 338 and 10 New Zealand 3rd Division. In the Pacific Islands Regiment, 54 Papua New Guineans had died on Bougainville. The Australian Army suffered 516 deaths after taking over from the Americans at Torokina. To these may be added the few army deaths in Bougainville before October 1944 and deaths in the Royal Australian Air Force and Royal Australian Navy. The total Japanese forces on Bougainville had numbered 65,000 in 1943. They had been reduced by death and disease by 23,000 or 24,000 during the year of American operations. In the months when the Australians had been expanding out of Torokina 8,500 Japanese had been killed and 9,800 had died of deprivation and illness. As 23,571 Japanese surrendered, over 40,000 Japanese and their volunteer and conscripted auxiliaries had died on Bougainville. By contrast less than 2,000 Allied servicemen had died.
For the Japanese and the Bougainvilleans the dying did not end with the war. The Australians did not have the transport or the stores and medicines to bring immediate relief, and they probably thought that their first concern was for the 14,000 Australians to be released from Japanese prisoner of war camps. While moving to, and being held at, temporary assembly points the Japanese were dependent on their own inadequate resources and they continued to die. Some Bougainvilleans suffered through 1946 as they waited for their gardens to come into production and for ANGAU and the new civil administration to respond to their needs.
Particular groups of noncombatants had suffered harshly. In the Marist Mission four priests, six brothers and two nuns had died. The impact of the war on Bougainvilleans can be gauged from the immediate post-war patrol reports and from the district census. A. J. Humphries patrolling south of the Luluai River in 1947 collected one Japanese, Lance-Corporal Matsingaga, and reported that the village population had dropped 42 per cent during the war. His figures did not, he said, include any children who had been born and died during the war. R. R. Cole who went north from the old government station at Kangu into the Mamaromino area in 1946 said that the pre-war population of 1,636 had been reduced to 1,083, and that there were many orphans aged between three and 14 in the villages. In Pariro where the people had not been supporting Japanese but just had Japanese foraging parties moving through, Humphries still found that the population had dropped by one-third. On the north-east coast few village books had survived but at Minsiveren the luluai (government appointed chief ) produced his book for C. W. Slattery who found that the 201 people of the pre-war were now reduced to 148. The district officer in his 1947/48 annual report thought that overall there had been a 20 to 25 per cent loss in population and that the greatest losses had been in the Kieta and Buin areas, and he noted that rehabilitation had been rapid. By then, he said, the field staff had paid just over £100,000 in war damage compensation to Bougainvilleans, and the despondency of the immediate post-war had almost gone.
The first comprehensive post-war census of 1950 confirmed the particular studies made by patrol officers. The total population of the Bougainville District was 41,190 and in 1940 it had been 49,067. That is a 16 per cent decline in population. But even that figure understates the impact of the war. The people of Bougainville suffered little deprivation until 1943 so the population was growing until then. It was probably over 52,000. By 1950 the recovery had already begun — the point of maximum decline may have been in 1946 when the population could have been under 40,000. If those figures are taken as the pre- and post-war totals then the fall was 25 per cent. And that one quarter decline took place after 1943.
Measured by the numbers of foreigners (three for every Bougainvillean) and the diversity of those foreigners; the amount of material landed on Bougainville; the demonstrations of the destructive capacity of mankind (they killed nearly 45,000 of each other); and the impact on the Bougainvilleans who joined, avoided and observed the war and lost a quarter of their number, then the war on Bougainville was as profound, disturbing and destructive as anywhere in the Pacific. The impact of the war on relations between Bougainvilleans was so profound that ceremonies of compensation and reconciliation for sides taken and things done continued until the late 1980s; and then the alliances and cleavages expressed within a world war were confirmed or swept aside in a civil war.