what was rapid about those societal reorganizations? how was society reorganized?
Rapid in they brought about massive changes in quick succession: the abolition of slavery and granting citizenship to black people wasn't a piecemeal, gradual process. Stuff like social security and the WPA was made possible by the Democratic supermajority of the time (and the circumstances under which they came into power); they weren't on the table just a decade earlier. The civil rights era undid 80 years of legalized segregation in 1/8th that time.
10 years for change is a slow, long, process. particularly for people who actually fought for it. that's not "quick succession" for changes, its long, hard work for people