The united states became a society of consumers in late nineteenth century. What was the key factor that made that possible? Simple answer

Companies were investing lots of money on advertising and offering shoppers more convenient ways to place orders. Since big companies were producing a big variety of products and fighting over customers, the prices were lowered which made it possible for even the lower classes to have the opportunity to make purchases.

The United States acquired land from France, Spain, and the Kingdom / dominated by the steel and oil industry

this is a pretty broad question and can be a pretty lengthy answer. since 1900, women have gained a lot more rights and have become active in the workforce. with women being in the workforce, men play a larger role in family life. many family tasks are shared between men and women, whereas, women used to be the sole family caretakers.

that should get you started at least.