Final answer:
The rise of the Republican Party was based on their opposition to slavery's expansion, promises of land and infrastructure development in the West, and a commitment to public schools and immigrant rights.
Step-by-step explanation:
The Republican Party, known at the time as the Democratic-Republican Party, rose to power on the promise of opposing the expansion of slavery and introducing reformative policies that would benefit the northern electorate. Their platform included the promotion of new land for Westerners, support for public schools, a protective tariff, a transcontinental railroad, and immigrant political rights.
During the contentious elections of the mid-19th century, this commitment, combined with avoiding the polarizing impacts of the ongoing sectional crisis, allowed them to gather support from a diverse range of voters.
The party's stance against slavery expansion was clear and consistent, highlighted by their condemnation of actions like John Brown's raid. They made substantial promises to their predominantly white constituents and aimed to appeal broadly by advocating for economic development that would stimulate growth and stability without undermining the values of individual freedom and limited government intervention desired by many of their supporters.