Ineed writing a thesis for an essay about how the conditions for the middle class improved in 1900s

Even though the early 1900s were a time when urbanization was growing like wildfire and cities were popping up all over the map, rural farming was still an important occupation of the working class. As factories and industries grew, farmers provided the food and agricultural resources that helped sustain life. The working class was often divided according to socioeconomic status with the wealthiest making up only a small percentage of the total labor force. Most of the working class struggled to make a decent living in factories, shipyards and farming communities.

The answer is crop yield.