Short answers, pulled from the story.
The Three Alls policy was a Japanese scorched-earth campaign in China during World War II, built on the principle of kill all, burn all, loot all. It targeted suspected guerrilla base areas and aimed to turn them into unpopulated zones known as mujin chiku.
The policy took full effect in the spring of 1941 and continued in diminishing form until March of 1945. Its most intense year was 1942, when General Yasuji Okamura's forces conducted large-scale mopping-up operations across North China.
Major General Ryūkichi Tanaka formalized the campaigns in 1940, and General Yasuji Okamura escalated them after taking command of the North China Area Army in July 1941. Emperor Hirohito had personally approved earlier annihilation campaigns in an order dated the 2nd of December 1938.
Japan launched the policy in retaliation for the Communist-led Hundred Regiments Offensive of August 1940, a large guerrilla assault on railways, bridges and mines in northern China. General Tanaka responded with a plan for the total annihilation of Communist base areas.
Estimates vary widely. Historian Mitsuyoshi Himeta put the toll at more than 2,700,000 civilian deaths, while Li Enhan estimated 3,180,000 massacred and 2,760,000 enslaved, and Chinese Communist records describe base area populations falling from 44 million to 25 million.
Yes, Japan applied a version of the policy, known as San Kuang, against Vietnam starting on the 9th of March 1945. A joint study by Vietnamese professor Văn Tạo and Japanese professor Furuta Moto later confirmed that Japan's wartime policies killed 2 million Vietnamese through starvation.