How was the progressive movement a departure from the national politics in the late nineteenth century?
The progressive movement was a departure from earlier national politics largely because it aimed to use the power of the government to improve the lives of average Americans.
Before the early 1900s, the government was generally not involved in trying to reform society. It generally (there were some exceptions like the Granger laws) stuck to a relatively laissez-faire or pro-business set of policies. With the progressive movement came the attitude that the government should be doing more to help everyone. It was at this point that there came to be a serious push for the government to be involved in reforms of all sorts.