On December 7, 1941, Japanese planes attacked Oahu's Pearl Harbor and the United States officially entered World War II. The devastating attack on American soil created widespread suspicion of Japanese living in Hawaii and on the U.S. continent. Apprehension increased when Hawaii was thought to be soon invaded by Japan. The AJA soldiers serving in Army or National Guard units throughout the territory were assembled into the Hawaii Provisional Battalion. On June 5, 1942, this new unit of 1,432 boarded the SS Maui and were sent to the U.S. mainland. After landing in Oakland, California, they were named the 100th Infantry Battalion (Separate) to denote that their battalion was an "orphan" and not attached to any other military unit. The 100th trained in Wisconsin, Mississippi, and Louisiana, and when suffering high casualties while fighting in Italy in 1944, needed replacements came from the 442nd RCT--AJA volunteers from Hawaii and the Japanese internment camps in the mainland U.S.

The 100th served in combat in Europe from September 1943 until May 1945, when Germany surrendered. Their battalion experienced a high number of casualties, earning them the name the "Purple Heart Battalion." On June 21, 2000, the Medal of Honor was awarded to 21 Japanese American soldiers from the 100th Infantry Battalion and the 442nd Regimental Combat Team. Later, on November 2, 2011, the United States Congress presented the highest civilian award bestowed by Congress, the Congressional Gold Medal, to the 100th Infantry Battalion (Separate), 442nd Regimental Combat Team, and Military Intelligence Service.

In 2006, IU Kokomo senior lecturer in English, Karla Stouse, took students from her course F200: Asian Cultures to Hawaii. After coming in contact with Ann Kabasawa, students met with and interviewed members of the 100th Infantry Battalion Veterans at their clubhouse in Honolulu. Inspired by those discussions, students designed a Peace Garden to honor the veterans, as well as internment camp victims and survivors of Pearl Harbor. The Peace Garden was built in 2008 on the grounds of Darrough Chapel Park in Kokomo, Indiana. In 2020, the Peace Garden was moved to Jackson Street Commons, an apartment complex for formerly homeless veterans located in downtown Kokomo.