Which main idea from Unit 2 had the greatest positive impact on

Which main idea from Unit 2 had the greatest positive impact on the United States? Come up with 2 reasons as evidence to support your claim.
Overview: America changed into an industrial power starting in 1890. Cities grew as people immigrated to the United States or moved from the countryside. This activity is to examine the impact of these changes on our nation during the early industrial period.
Task: Write a two-paragraph discussion post answering the following question: Which main idea from Unit 2 had the greatest positive impact on the United States? 
Be sure to:1. Explain your choice AND Include 2 or more detailed pieces of evidence. You can use evidence from the lessons in this unit or from a credible outside source.2. Respond to another student.
How to Complete This Assignment:
Step 1: Choose ONE of the following topics from Unit 2. Which one do you think made the biggest impact on America during the early Industrial period?· Industrialization· Immigration· Urbanization· Imperialism
Step 2: Research your topic and take notes. You can use the lessons from our course, or outside sources. Here is a list of a few websites you can also use: 
Readings: 
Early Industrialization in the Northeast
Overview of the Gilded Age
Authentic History Center Galleries on Industrialization, Progressivism, and Imperialism
Videos: 
The Industrial Economy
Growth, Cities, and Immigration
American Imperialism
Skyscrapers and Steel Forge the Modern City 
Step 3: Write your post in two detailed paragraphs of 4-6 sentences each. Remember, your goal is to explain your choice and support your argument with two pieces of evidence. Good evidence is a detailed example from history, a descriptive quote or a statistic. You may use the following format to help you write your response: Outline/Format