Well, the earliest war during the twentieth century was World War I, but if you're asking about 1900 specifically, I'm not sure if there was any officially declared war that the United States was involved in. Later, World War II and the Korean and Vietnam Wars ensued.
Changes in manufacturing in the late 1700s and early 1800s greatly affected people living in cities in the North in that an increase in manufacturing due to the Industrial Revolution led to a great increase in the number of jobs available, which increased the standard of living for many citizens.
The Great society was composed of different democratic programs which aims to eliminate the surgence of poverty. This program was launched by President Lyndon Johnson. although he implemented the Great Society under his rule, it was John F. Keneddy's initiatives called the "New Frontier" where the programs are rooted from
Don't have to deal with racism.