World War II: Japanese high command orders withdrawal at Milne Bay, the first major Japanese defeat in land warfare during the Pacific War.

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 Battle of Milne Bay, also known as Operation RE or the Battle of Rabi (ラビの戦い) by the Japanese, was a battle of the Pacific campaign of World War II. Japanese naval infantry, known as Kaigun Tokubetsu Rikusentai, with two small tanks attacked the Allied airfields at Milne Bay that had been established on the eastern tip of New Guinea. Due to poor intelligence work, the Japanese miscalculated the size of the predominantly Australian garrison and, believing that the airfields were defended by only two or three companies, initially landed a force roughly equivalent in size to one battalion on 25 August 1942. The Allies, forewarned by intelligence from Ultra, had heavily reinforced the garrison.

The Pacific War, sometimes called the Asia–Pacific War or the Pacific Theatre, was the theatre of World War II fought between the Empire of Japan and the Allies in East and Southeast Asia, the Pacific and Indian Oceans, and Oceania. It was geographically the largest theatre of the war, including the Pacific Ocean theatre, the South West Pacific theatre, the Second Sino-Japanese War, and the brief Soviet–Japanese War, and included some of the largest naval battles in history. War between Japan and the Republic of China had begun in 1937, with hostilities dating back to Japan's invasion of Manchuria in 1931, but the Pacific War is more widely accepted to have begun in 1941, when the United States and United Kingdom were brought into the war, after being attacked by Japan.