What events slowed the growth in population from 1930 to 1940

The stock market crash of 1929 was the catalyst that brought about the Great Depression that lasted until around 1939.

Explanation:

As a result of the fall of the stock market, consumer spending decreased, industries slowed production, and unemployment rates steadily increased. Instead of people migrating to the area, people were leaving in search of work, etc. More women joined the workforce (which would’ve also had an effect due to lower marriage and birth rates).

i believe george gallup used a poll in 1936