Complex sentence: More than 110,000 Japanese Americans, who mostly lived on the West Coast, were forced into interior camps, but in Hawaii, where the 150,000-plus Japanese Americans composed over one-third of the population, 1,200 to 1,800 were interned.
Split into simpler sentences: More than 110,000 Japanese Americans in the mainland US, who mostly lived on the West Coast, were forced into interior camps. However, in Hawaii, where 150,000-plus Japanese Americans composed over one-third of the population, only 1,200 to 1,800 were interned.