The most influenced by the growth in my opinion would be the women.
Women were beginning to take on roles other than the typical housewife. Many were servants and others worked in factories. Still a far cry from equality! Speaking of equality, things got worse for African Americans in the beginning of the 1900's they had less power and were more divided from whites than ever before. The most secure people at this time in history and for years to come were the middle class whites, they enjoyed a secure social position and economic status. .
With the ever growing areas of industry and technology many jobs were becoming available, but with no room for ever advancing in many cases and very few rules. Many employed women and children. They had long hours, little pay and harsh working conditions. This began to change with many formed organizations such as Labor Unions and ethnic organizations. .
With all this growth the government seemed weak and limited; something had to be done to change this. By 1900 an activist presidency began to emerge and the Republicans dominated it. President Woodrow Wilson began to expand our involvement in world affairs and moved America into a powerful position. Things began to look up. Americans responded by helping others in different ways. In areas of conservation and preservation and religion many organizations were formed. One of the biggest goals was to insure national security, but with this goal came disputes with European colonial powers. These conflicts and the beginning of World Trade, the United States and its rise in power resulted in a World War. Although the government claimed to want to stay neutral we eventually ended up right in the middle of World War I. In my opinion there was never an effort to stay neutral; the government just wanted the public to think so. It seemed to be trend, as we see later with the disillusionment of the public as far as actual money in the stock market in the 1920's.