World War II: The Matanikau action on Guadalcanal begins: U.S. Marines attack Japanese units along the Matanikau River.

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 Actions along the Matanikau—sometimes referred to as the Second and Third Battles of the Matanikau—were two separate but related engagements between the United States and Imperial Japanese naval and ground forces in the Pacific theater of World War II. The actions occurred around the Matanikau River on Guadalcanal Island in the southwestern Pacific during the Guadalcanal campaign. These particular engagements—the first taking place between 23 and 27 September, and the second between 6 and 9 October—were two of the largest and most significant of the Matanikau actions.

Guadalcanal is the principal island in Guadalcanal Province of Solomon Islands, located in the southwestern Pacific Ocean, northeast of Australia. It is the largest island in the Solomons by area and the second-largest by population. The island is mainly covered in dense tropical rainforest and has a mountainous hinterland.

The Matanikau River of Guadalcanal, Solomon Islands, is located in the northwest part of the island. During the World War II Guadalcanal campaign, several significant engagements occurred between United States and Japanese forces near the river.