Because it had a great effect on history.
The Nazi's Final solution was implemented to rid Germany of C) Untermenschen.
This policy was called "containment" - the idea was to contain communism from spreading to new countries without trying to actively challenge the communist system in the countries that already had it.
This policy lead to some proxy wars, in which the US fought the Soviet Union for the free countries.
After the Civil War, many newly freed slaves migrated to the west because of the the Homestead Act that was passed in the year 1862. his act promised free land to all the settlers. 160 acres of free land or at a minor cost was promised to all those that settled in the west and had no criminal cases lodged against them for acting against the government of the United States.
