Final answer:
The agricultural industry did not see huge gains during the 1920s due to overproduction and falling crop prices, which contributed to the economic weaknesses leading to the Great Depression.
Step-by-step explanation:
The part of the American economy that did not see huge gains during the 1920s was the agricultural industry. While other sectors like manufacturing and finance experienced significant growth, the agricultural industry struggled due to overproduction and falling crop prices. This led to financial difficulties for farmers and contributed to the economic weaknesses that eventually led to the Great Depression.