What were three major aspects of industrialization between 1865 and 1920?

Three major aspects of industrialization in this period include the increase of large factories, laissez faire policy (literally "let do" in French), and a rise in the proletariat—the availability of large numbers of workers.
The increases in large factories are closely linked to the idea that everyone should have access to the same decent way of living. To make products more accessible to everyone, they needed to be cheaper—cheaper means mass production (and fast production so companies don't lose profit). Society was also shifting towards the idea of consumerism, which enabled the growth of large factories and mass production systems (e.g., Ford industries).
This mass production would have been impossible were it not for an increase in workers in urban areas. Mass production required workers to have very little to no education, which made it easier to hire many people to produce massively. This rise of workers in the urban areas occurred as agriculture became more dependent on technology rather than human resources. However, immigration into the United States also played a part during these years.
As to laissez faire, it means exactly what it says: "Let do." This policy meant that the government stood back and did not overly influence the economy or choices of businesses. Businesses were free to do quite as they pleased, and very few governmental regulations were set in place—mostly to the benefit of US businesses.