What's the importance of The 442nd Nisei Combat Unit in terms of WWII?
This combat unit was important in the history of World War II because it was made up of Japanese Americans. Many of the men in this combat unit had been recruited out of the internment camps that they had been put into soon after the war began. The 442nd fought in Europe and became one of the most decorated units in the war. It even had a movie made about it -- "Go For Broke." (This was the unit slogan.)
Perhaps the most famous veteran of the 442nd is the long-time US Senator from Hawaii, Daniel Inouye. He lost an arm fighting in Italy and was awarded the Medal of Honor.
Actually, the 442nd is the most decorated unit in US military history, not just World War II, with seven Presidential Unit Citations and 21 Congressional Medal of Honor winners. Since it was made up of Japanese-Americans who had been born in the US, there was an extra incentive and motivation for those soldiers to prove themselves and their loyalty to America. Some might say it made them take chances and fight harder than ordinary units.
Japanese-American units were forbidden to fight in the Pacific, and so the 442nd fought almost exclusively in Italy during the war.