I would split it up between in 1930's and 1960's to 70's.

The 1960's and 70's saw the biggest social unrest in the US by far.

You had assassinations or attempts of public figures such as JFK, RFK, George Wallace, MLK, Malcolm X, Medgar Evers, and Harvey Milk all in a 20 year span.

You have Hundreds of riots with thousands killed or injured. Important riots such as the gay Stonewall Rights , Harlem Riots of 64, the MLK assassination riots that where cross country, Detroit Riots, Newark Riots,the Watts Riots, and the 1968 democratic convention to name a few.

You have the collapse and reorganization of the Republican and the Democratic party with 10 years. in 1964 Goldwater lost 486 to 52 in the presidential election, in 72 not 8 years later Nixon won 520 to 17.

You had Massive Anti-war rally's in Washington, Sit-ins on hundreds of campuses, attack/bombings of military and government offices such as draft boards. You had National guard shooting in Kent state.

You had the progressive push of Johnson's Great Society, Nixon's EPA, the end to segregation, Busing, Affirmative Action, the end of the draft, and the most controversial to this day Roe Vs Wade. You had the backlash to progressive pushes in the defeat of the National Equality Act, the rise of Anti Unionism, and the rise of the new republican Party starting with Reagan/Goldwater.