Question

In the era after world war i and before the great depression, american suburbs began to grow rapidly because of

Answer 1

Because it was deemed safer than city life. Also the war put a great stunt on population growth and once it came to an end people began having more kids than ever before hence the name "baby boomers". Suburbs proved more suitable for family like and rose to popularity in the post World War 1 society. 

Answer 2

Mass production of automobiles. The mass production of automobiles caused for inexpensive cars to be available, making the move into american suburbs possible.