What was the only part of the current United States invaded by the Japanese during WWII?

In June 1942, six months after the attack on Pearl Harbor, Japanese forces landed on and occupied two islands in the Aleutian chain, marking the first time American soil had been occupied by a foreign power since the War of 1812. The remote, windswept islands of Attu and Kiska became the unlikely setting for a brutal, year-long conflict. This northern invasion was partly a diversionary tactic, intended to draw a portion of the U.S. Pacific Fleet away from the main Japanese offensive at the Battle of Midway. The Japanese also sought to establish a defensive barrier in the North Pacific to prevent the U.S. from using the Aleutians as a base for attacking Japan.

The campaign to reclaim the islands is often called the "Forgotten Battle," as it was overshadowed by other major events in the war. American and Canadian forces faced not only a determined enemy but also the harsh, unforgiving Alaskan weather. In May 1943, U.S. troops landed on Attu and engaged in a bloody, three-week battle that resulted in high casualties on both sides. Proportionally, the Battle of Attu was one of the deadliest battles in the Pacific Theater.

When Allied forces later moved to retake Kiska in August 1943, they made a surprising discovery. After a sustained three-week bombardment, a large invasion force of American and Canadian soldiers landed on the island, only to find it empty. Under the cover of dense fog, the Japanese had successfully evacuated their entire garrison just weeks before. The occupation also had a tragic impact on the local Unangax̂ (Aleut) people of Attu, who were captured and taken to Japan as prisoners of war, where many died from disease and starvation.