Why are there mostly white people in Alaska?

There is actually a smaller percentage of white population in Alaska than in the whole of the US. The US Census Bureau Demographics for Alaska, 2009 (most recent reported) are:

66.7% White

03.3 % Black

21.2% Native, Asian, Pacific Islander

08.8% other (incl. mixed and unreported)

The US Census Bureau demographics for the 50 US states, 2009 (most recent reported) are:

72.4% White

12.6 % Black

05.9% Native, Asian, Pacific Islander

09.1% other (incl. mixed and unreported)

The widest variation in the numbers is the difference between the Native, Asian, Pacific population and the Black population.