Answer: "The urbanization of the United States quickened due to technology improvements. Without innovations in food production, the factories could not have grown so quickly. The trend quickened after 1860 and continued throughout the 21st century as well. By 2007, more Americans lived in or near cities than they did in rural areas." Because it just in one the previous sentences it already said that food was aplenty.
Explanation: But you could remove "As a result, cities grew in numbers of people and physical space. As more people and businesses moved in, they needed buildings for living and working. They needed ways to move around the city. We call this process urbanization." because after it talks about the population already being grown.