Final answer:
The Republican Party's unique characteristics included their strong stance against the expansion of slavery, their debates on the size and scope of the federal government, and their broad appeal to various groups of constituents.
Step-by-step explanation:
Three characteristics that made the Republican Party unique when it became one of the two major parties in the national politics were its opposition to the expansion of slavery, internal debates regarding the role of the federal government, and strategic positioning to appeal to a wide variety of constituents including former Democrats former Whigs nativists and immigrants.
- The antislavery platform was a core issue for the Republicans, uniquely positioning them in contrast to other parties of the time with their strong moral stance against slavery's expansion into new territories and states.
- The party's internal divisions, particularly those who formed the Liberal Republicans, sparked debates on limiting the federal government's size and scope, therefore shaping the national discourse on government intervention and Reconstruction efforts.
- The Republicans managed to broaden their constituency by packaging their views in a way that appealed to a diverse group of voters, which was crucial for political success during and after the tumultuous period leading up to the Civil War.