Final answer:
The American party system experienced significant changes due to the Democratic Party's support for civil rights under President Lyndon Johnson. Southern whites shifted loyalty to the Republican Party, African Americans started voting for Republicans, and northern liberals left the Democratic Party to support Republicans.
Step-by-step explanation:
The American party system underwent significant changes due to the Democratic Party, under President Lyndon Johnson, supporting the Civil Rights Act of 1964 and the Voting Rights Act of 1965. As a result, the loyalty of southern whites shifted from the Democratic Party to the Republican Party. This realignment was prompted by southern Democrats' opposition to the national government's efforts to promote racial integration and social welfare. The Republican Party, with its pro-business platform and opposition to encroachment of the national government into state and local matters, attracted many southern whites.
Additionally, African Americans began voting for Republicans at high rates for the first time. This shift occurred because the Democratic Party's support for civil rights showed a willingness to address racial equality, which appealed to African American voters. African Americans had previously supported the Republican Party, the party of Lincoln, but the Democrats' commitment to civil rights caused a change in their voting patterns.
Furthermore, while not explicitly mentioned in the options, the support for civil rights by the Democratic Party under Johnson led to disenchanted northern liberals leaving the Democratic Party and consistently voting for Republicans. They felt that the party was not progressive enough on important social issues, such as civil rights, and sought a more liberal alternative in the Republican Party.
In summary, all of the above statements are true. The Democratic Party's support for the Civil Rights Act of 1964 and the Voting Rights Act of 1965 led to southern whites shifting their loyalty to the Republican Party. African Americans began voting for Republicans at high rates, and northern liberals left the Democratic Party and started voting for Republicans.