The greatest area of world war 2 population growth and expansion of defense industries was the

The west coast of the US had the largest growth in both these metrics. This is mainly because of the need for defenses against invasion by Eastern countries, which led to the increased need for defensive industries. Also, with the number of people from those same countries interred in the camps up and down the west coast, the population tended to grow at a quicker pace, as well.

To be honest i thinks its between the first answer and the third answer