The 100th Infantry Battalion combined with a regiment composed of men of Japanese ancestry who fought primarily in what war?
100th Infantry Battalion (United States):  The 100th saw heavy combat during World War II before and after combining with the 442nd Infantry Regiment, another mostly Nisei military unit, into a single fighting combat team. 442nd Infantry Regiment (United States):  The regiment was a fighting unit composed almost entirely of American soldiers of Japanese ancestry (mostly from Hawaii) who fought in World War II.
World War II