Identify two factors that encouraged the growth of the suburbs in the mid 1900s

1.  Homes in the suburbs were affordable to middle class families.  This had to do with lower land prices in suburbs vs. the city and also new building practices that brought down the cost of these suburban homes.

2.  The G.I. bill provided loans to military veterans, so this also helped them be able to afford "the American dream" of home ownership.

3.  The construction of highways facilitated travel into the cities for work from the suburbs.  (Note that the Federal Aid Highway Act was passed in 1956.)

4.  There was a perception that life in the suburbs would be safer and less susceptible to crime than life in the city.

That's several reasons you can work with.