The United States has become much more modern in the time since 1877. The most important examples of this are seen in the rise and spread of democracy and civil rights in the United States.
In 1877, the United States was dominated by white, male, Protestants. Other types of people were either looked down upon and/or treated as second-class citizens in the eyes of the law. Since 1877, the country has become much more inclusive. This move away from racism and sexism is one of the most important ways in which the US has become more modern.