In the United States, Progressivism has been associated with sets of (normally left leaning relative to the political spectrum of the time) political reforms whose number and societal effect were noticeable in the time period. These reforms have been traditionally tempered, or opposed by - normally right wing or right leaning- groups called Conservatives.
The opposite of Progressivism, from this standpoint, seems to be Reactionary reforms. That is, a (typically) right-wing movement that gains historical notoriety by the number of reforms overturned, or reforms antithetical to Progressive ideas enacted, with comparable societal effect and number as a Progressive movement would be. However, unlike in the general Progressive-Conservative dynamic I mentioned in the first paragraph, I have not heard of the countervailing political movement during a Reactionary period That is, I do not know the second political term that would accompany a Reactionary-??? Dynamic.
Given the political dynamics explained above, what is the term for the countervailing political movement to Reactionism that would be analogous to the "Conservative" counter-weight of a "Progressive-Conservative" dynamic?