Complex sentence: The average income of a Native American increased to $2,500 by 1944,2.5 times greater than in 1940, the average salary of a Native American was still only quarter of the average salary of a white American.
Split into simpler sentences: The average income of a Native American increased to $2,500 by 1944,2.5 times greater than in 1940. However, the average salary of a Native American was still only a quarter of the average salary of a white American.