How and when did the major U.S. political parties realign on race and civil‑rights issues during the 20th century?

1. Early currents: migration, the New Deal, and organizational pressure

Black political affiliation began changing well before the 1960s as the Great Migration relocated millions of Black voters into Northern cities where New Deal benefits and labor alliances made the Democratic Party an increasingly attractive home; scholars trace NAACP and labor group pressure inside the Democratic coalition as key engines of that early shift ^{[1] [7] [6]}. Congressional and party elites resisted acknowledging these shifts for years, but historians argue that changes in urban demographics and organized interest‑group activity created a bottom‑up movement of Black voters toward Democratic institutions by midcentury ^{[5] [6]}.

2. Mid‑century turning points: Truman through Johnson

Federal actions in the 1940s–1960s—Truman’s military integration and, most consequentially, Lyndon Johnson’s championing of the Civil Rights Act and the Voting Rights Act —transformed national party positions on civil rights and signaled to voters which party would defend legal racial equality at the federal level ^{[1] [8] [5]}. These policy commitments polarized activists and elites on race-related issues and, according to classic political‑science accounts, sent clear signals that accelerated partisan sorting on civil‑rights attitudes ^[3].

3. The Republican reaction and the Southern turn

As Democrats nationally embraced civil‑rights legislation, many white Southern Democrats felt alienated; Republican leaders such as Barry Goldwater in 1964 (who opposed the Civil Rights Act on libertarian grounds) and Richard Nixon in 1968 pursued strategies that appealed to white Southern and conservative voters through “states’ rights” and cultural messaging—moves scholars label the “Southern strategy” and credit with shifting large numbers of white Southerners to the GOP ^{[4] [9]}. That top‑down strategic appeal intersected with existing regional resentment over federal enforcement of civil rights, producing a durable regional realignment even as congressional control changed more slowly ^{[4] [3]}.

4. When was the realignment — a single break or a long fuse?

There is scholarly disagreement: some treat 1964 as an “issue‑based realignment” because elites and activists polarized sharply then and public partisan identities shifted quickly on race ^[3], while others caution that demographic movements, local politics, and decades of party evolution made the change gradual and contingent rather than a single switch ^{[5] [6]}. Recent work—emphasizing the Great Migration, NAACP and labor organizing, and congressional maneuvering—argues the groundwork for the modern racial parties was laid well before national legislation forced elites to choose sides ^{[7] [6] [5]}.

5. Legacy: coalition geography and the culture wars

By the late 20th century the durable pattern was clear: Black Americans became a core Democratic constituency and white Southerners a central Republican base, a division that reshaped regional politics and undergirded later cultural‑issue polarization; analysts link today’s culture wars to this racial realignment because attitudes on race cohered with other cultural issue positions long before parties fully embraced them ^{[6] [9]}. While dominant narratives emphasize elite strategies like Nixon’s, recent scholarship stresses that migration, interest‑group pressure, and northern Democratic transformations were equally decisive in producing the century’s partisan map ^{[5] [6]}.

Limitations: this account relies on the cited scholarship and summaries provided; it does not adjudicate every contested archival claim and omits some county‑level electoral evidence not included in the sources provided ^{[5] [3]}.