Why was the populism movement important?
it paved the way for later reform movements.
it strengthened the power of the federal government.
it caused farmers to move to the cities in search of jobs.

d is the best answer for this question.

i believe it would influence their own way of understanding things. it shall be a foundation where they can draw or start an argument.   historians are also  scientists that  have their tools of analysis and expertise to unlock a variety of difficulties such as relationships of man, origin, politics, economy, and culture. based on facts and understanding on these areas, they may shade light to extract ideas and develop options to validate a hypothesis or debunk it.