The United States has grown in many ways since the Civil War. We have equal rights. Blacks and Whites are equal, as are men and women. The United States is also considered to be the "melting pot" of the world. Meaning that there are many different cultures and religions and everyone can get along.
The citizens of 1930s Germany and 1970s Cambodia dealt with ruthless dictators and corrupt, vicious governments. The Nazis and the Khmer Rouge turned their countries into police states, with frequent arrests and violence.