What transformed us politics in the 1920’s?

a. the return of the republican old guard

b. the ascent of progressive politicians

c. rising support for the democrats

d. a split in the democratic party

the answer is D, A split in the democratic party :)

A. The return of the republican old guard  

Explanation:

In the race of 1920, the Democratic applicant firmly upheld the League of Nations. Then again, the Republican competitor Warren Harding restricted it. His motto was "a return to normalcy" which implied an arrival to the conditions before the war. He needed to come back to noninterference, and not to think about foreign issues. He won the election.