Had to manage and defend his land and those who worked in that land. When the lord (or vassals since they're local lords) is provided land by the king in exchange for loyalty, providing military service and military protection. It is the vassal's responsibility to manage the estate well and is given the authority to rule over the land and over those who lived in that land (peasants and serfs).
Explanation: Isolationism is a term that designates a political and diplomatic situation in some territories that have chosen to keep their society literally isolated.
Main cause communism. The north did not want to adopt communism while the south did hence the reason for why the US got involved to make sure that the north would win so as to help stop the spread of communism (sorry i know this is kind of late)