The Manifest Destiny was the belief that America need to expand its borders. This shaped the use due to the fact that if caused many disputes among the natives and Mexicans that controlled most of the land that was unclaimed.
Tons of racial violence went on during the 20th century, including but not limited to lynching, rioting, looting, and even killing. The early 20th century was known for its segregation and racial violence.
Before the agricultural revolution much of England's farmland was "common" land, since there was far less competition in terms of the land being used for crop cultivation.
1. Cold war
2. Division of Germany
3. Emergence of two superpowers - U.S and Soviet Union
4. United Nations