Final answer:
Two groups came together to pass the Civil Rights Act of 1866: Radical Republicans and Democrats. This act was crucial in the early establishment of civil rights for African Americans after the Civil War. Furthermore, the Second Party System was characterized by the political rivalry between Democrats and Whigs.
Step-by-step explanation:
Which two groups came together to pass the Civil Rights Act of 1866? The correct answer is A. Radical Republicans and Democrats. This act was one of the early efforts to establish equal rights for African Americans, coming in the tumultuous period after the Civil War. While the Democrats were largely against the act, enough joined the Radical Republicans in passing it over President Andrew Johnson's veto.
The Republican Party, particularly the Radical Republicans, was most concerned with securing civil rights for formerly enslaved people, as indicated by option A in the related concern from 1864 and 1865. It's also worth noting that during the Second Party System, the two main political parties were Democrats and Whigs, which is represented by answer C from Exercise 12.3.1 and Test Yourself question.
Following the Civil War, the Republican majority in Congress was outraged by the actions of the reconstituted southern states' governments and hence focused on legislation aimed at protecting freedmen and reconstructing political relations in the South, forming a new powerful voting bloc of African Americans in the process.