After Pearl Harbor happened for the US in WW II, the US got very scared that there were spies from Japan in the US (It was said that there were spies in Hawaii during Pearl Harbor), so they literally only took Japanese-Americans from the west coast of the US (places like Cali,Oregon,Etc) to places called interment camps, this was just to make sure that none of these people were spies and they couldn't do anything. Many of the people taken in these internment camps were US citizens, but if you had one family member with heritage from Japan, you were taken to an internment camp.
With the development of the machine gun, a "no man's land" was established between the Allied and Axis trenches. Neither army could advance without sustaining enormous casualties.
