'Sanko' was the Japanese 'scorched earth' offensive in the five north-eastern provinces of China in the aftermath of the 'Hundred Regiments' communist offensive (1942/44).

This so-called 'Three Alls' offensive, so named as its method was 'kill all, burn all and loot all', was initially schemed in 1940 by Major General Ryukichi Tanaka, chief-of-staff of Lieutenant General Yoshio Shinozuka’s 1^st Army, and was fully implemented from 1942 in north-eastern China by General Yasutsuga Okamura’s Northern China Area Army, comprising General Teiichi Yoshimoto’s 1^st Army, Lieutenant General Ichiji Dobashi’s (from 1 March 1943 General Seiichi Kita’s) 12^th Army and eventually Lieutenant General Tadayasu Hosokawa’s 43^rd Army as well as the 2^nd Independent Mixed Brigade.

Following the receipt of official authorisation from Tokyo in December 1941, Okamura categorised the Hebei, Shandong, Shensi, Shanhsi and Chahaer provinces into 'pacified', 'semi-pacified' and 'unpacified' areas, and launched his forces into the area, burning villages, seizing grain, and forcibly conscripting the local peasantry to construct collective hamlets. The 'three alls' policy also involved the creation of vast trench lines, thousands of miles of containment walls and moats, watchtowers and roads. These operations were designed to facilitate the destruction of 'enemies pretending to be local people' and 'all males between the ages of 15 and 60 whom we suspect to be enemies'.

It is now reckoned that more than 10 million Chinese civilians were mobilised by the Japanese army as forced labour in north China and Manchukuo. One estimate has suggested that the 'three alls' policy, personally sanctioned by the Emperor Hirohito, led to the deaths of more than 2.7 million Chinese civilians including some, it is claimed, who were the targets of chemical warfare.