World War II: The Allies bombard Bangkok, leading Thailand, then under Japanese control, to declare war against the United States and United Kingdom.

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 city of Bangkok, Thailand was bombed by the Allies on numerous occasions during World War II. It was also the target for the first combat mission by Boeing B-29 Superfortresses in June 1944.