((it's a college class,by the way))What are some history books about America after 1865?
Well this is a good college level textbook for history and government, that I personally read.
American Government, Ninth Edition
James Q. Wilson
John J. DiIulio, Jr., University of Pennsylvania
There is also an online site that I shall post below containing the notes and outlines for the book with study material. You can opt to use the website over the actual book if you want to save time and money.