During World War II the Japanese foot soldiers invaded a land region that is today part of United States. What is it?

It's a little-known chapter of the Pacific War, but in June 1942, Imperial Japanese forces invaded and occupied two remote islands in the Aleutian chain: Attu and Kiska. At the time, Alaska was a U.S. territory, making this the only instance during the war where enemy soldiers captured and held North American soil. This occupation marked the first time a foreign military had controlled U.S. territory since the War of 1812.

The Aleutian Islands Campaign was not intended as a prelude to a mainland invasion. Instead, it served as a strategic diversion. The Japanese high command hoped that by attacking in the north, they could draw a portion of the U.S. Pacific Fleet away from their primary target: Midway Atoll. While the diversion failed to impact the decisive American victory at Midway, the Japanese occupation of the two islands lasted for nearly a year.

The fight to reclaim the territory was long and brutal. A joint force of American and Canadian soldiers battled not only the entrenched Japanese defenders but also the region's notoriously harsh weather of dense fog and freezing winds. The 1943 Battle of Attu was one of the deadliest battles of the war on a per-capita basis, earning the Aleutian campaign the nickname "The Forgotten Battle."