Second World War: The Japanese occupation of Hong Kong began when Mark Aitchison Young, the Governor of Hong Kong, surrendered the territory to Japan after 18 days of fierce fighting.

World War II or the Second World War was a global conflict between two coalitions: the Allies and the Axis powers. Nearly all of the world's countries participated, with many nations mobilising all resources in pursuit of total war. Tanks and aircraft played major roles, enabling the strategic bombing of cities and delivery of the first and only nuclear weapons ever used in war. World War II is the deadliest conflict in history, causing the death of 70 to 85 million people, more than half of whom were civilians. Millions died in genocides, including the Holocaust, and by massacres, starvation, and disease. After the Allied victory, Germany, Austria, Japan, and Korea were occupied, and German and Japanese leaders were tried for war crimes.

The Japanese occupation of Hong Kong began when the governor of Hong Kong, Mark Aitchison Young, surrendered the British Crown colony of Hong Kong to the Empire of Japan on 25 December 1941. His surrender occurred after 18 days of fierce fighting against the Japanese forces that invaded the territory. The occupation lasted for three years and eight months until Japan surrendered at the end of the Second World War. The length of the period later became a metonym of the occupation.