Which primary source document could a historian understand why the us civil war started

:) during the cold war, people were afraid of communists, both outside and inside the united states. the red scare and mccarthyism that grew out of these fears were damaging to the american way of life. during the mccarthy years, many of the freedoms guaranteed in the bill of rights were limited. write a paragraph explaining what lessons can be learned from the mccarthy era about what u.s. citizens need to protect in order to preserve the democratic political system and the american way of life.